Ulrich Hohenester

News (2009 - 2010).

12.12.2014 : MNPBEM toolbox -- substrates and layer structures

It might be too early for a Christmas gift. Yet, for those who have previously used our Matlab toolbox for the simulation of plasmonic nanoparticles there are good news: the new version MNPBEM14 is available.

It now includes substrates and layer structures (not yet for EELS simulations) as well as many new features.  The toolbox also contains a detailed Matlab help (for the installation see Readme.txt in the main directory) and a number of demo files.

The toolbox can be downloaded here.  For the download one must provide a name and a valid e-mail address. We recommend changing to the new version.  Programs that ran under MNPBEM11 and MNPBEM13 should also run under MNPBEM14, maybe subject to a few minor changes.  We are currently writing a paper about our implementation of layer structures, however, for the moment the help pages and demo files should provide sufficient information.

17.10.2014 : Dark becomes darkish

In 2012 Franz Schmidt and coworkers (including myself) published a paper in Nano Letters with the title "Dark Plasmonic Breathing Modes in Silver Nanodisks", where we mapped the complete plasmonic spectrum of silver nanodisks by electron energy loss spectroscopy and showed that the mode which couples strongest to the electron beam has radial symmetry with no net dipole moment. As concluded in the abstract, this mode does not couple to light and has escaped from observation in optical experiments.

Austrians have the tendency of questioning strict rules. For instance, if something is strictly forbidden one would still seek for ways of achieving the forbidden thing, not in a straight but rather in a kind of detour way. So it was natural for us to ask: "What can we do to observe an optically forbidden mode in an optical experiment?" Oblique incidence of the exciting light and larger plasmonic nanostructures proved sufficient to observe the breathing modes in extinction spectra, thus turning the dark modes to darkish.

The measurements were performed by Markus Krug within his master thesis, and he worked hard to maneuver around the inittial problems of single-nanoparticle measurements and inhomogeneities of nanoparticle arrays. Markus was accompanied by Michi Reisecker from my group (see also News of 17.06.2014) who performed extensive simulations, and together they collected a huge body of evidence that was finally written up by Jo Krenn. The paper had a smooth refereeing process and has now been accepeted for publication in Applied Physics Letters. Thanks a lot to all co-authors for this beautiful collaboration !!

10.09.2014 : GRAPE vs. Krotov

Optimal quantum control deals with quantum systems that can be controlled through external control fields, such as laser pulses for molecules or magnetic microtraps for Bose-Einstein condensates (BECs). "Optimal" refers to optimal control theory (OCT), which allows to devise optimized control fields in order to achieve user-defined control targets.

We have applied OCT to BECs for quite a while, mostly in collaboration with the Schmiedmayer group (TU Vienna), and have successfully demonstrated wavefunction splitting and shaking. In a paper that has just been accepted for publication in Phys. Rev. A, we now compare in collaboration with the group of Christiane Koch (Kassel) the performance of different OCT implementations. Within our gradient ascent pulse engineering (GRAPE) scheme, we start with a control guess and employ OCT to compute the search direction for an improved control field. How much the control is finally changed along this search direction is determined by a generic and black-box linesearch algorithm. In contrast, the Krotov algorithm is constructed such that within one OCT iteration a new control field is computed which automatically leads to a better performance.

Which one of the two techniques works better? Our answer is ambiguous. On the one hand, Krotov has the advantage that the cost function, quantifying the control target, decreases within each iteration, thus leading to fast convergence. Unfortunately, fast convergence is often accompanied with sharp features in the control fields, which are unfavorable for many experimental implementations. Such sharp control features are absent in our GRAPE optimization. The prize to be paid for that is a computationally rather costly linesearch where one determines how much the control is modified along a given search direction. In our paper we systematically investigate the pros and cons of the two approaches.

I am thankful to Georg Jäger, who was the leading person behind this study and spent many hours devising significant figures. Working together with Christiane Koch, who is one of the leading experts of Krotov, and her group has been a true pleasure. Refereeing has been extremely smooth, with two rounds where our pertinent but critical reviewer responded always within two days (!). I must say that I like our final piece of work, and I thank all collaborators for this joint endeavor.

04.09.2014 : NFO-13


From  31.08.-04.09.2014 I attended the NFO-13 conference on near-field optics, nanophotonics and related techniques in Salt Lake City, USA. It has been an extremely interesting meeting with about 300 participants, with a lot of interesting contributions and a strong focus on imaging of life science at the nanoscale. Contrary to what one could expect, Utah, particularly the Salt Lake City area, has recently seen the rising of many interesting micro-breweries, so the conference has been great also from a social point of view.

On the other hand, it has been hard to be located in the beautiful scenery of Snowbird within the mountains, and to be captured in the conference site for the entire week. Finally, on the last day after the ending of the conference (and before the gala dinner with cool bluegrass music) I was able to climb together with Jeremy Baumberg from Cambridge university the Utah Twin Peaks (3502 m) nearby the conference site.

PS: The plenary talk of the conference has been given by Eric Betzig, one of the laureates of the 2014 nobel prize in Chemistry.

12.08.2014 : Mag. Andreas Kleinbichler

Andi Kleinbichler
Andi KleinbichlerOn August 12, 2014 Andi Kleinbichler finished his final diploma exam with distinction. His thesis (8.5 MB) "Periodic structures of metallic nanoparticles" was concerned with the simulation of arrays of plasmonic nanoparticles, using the MNPBEM Toolbox. The original motivation for this thesis goes back to the interest of an Austrian company who was interested in such simulations. Unfortunately, soon after Andi started they lost interest but we decided to continue with the code development.

Altogether, I have been very happy with his performance. Andi is a careful worker and has been extremely patient in navigating through the various difficulties that emerged during his thesis. He also had a good feeling of when to get support from me or other group members, which helped him to bring the implementation of periodic arrays to a successful end. I apologize for the pictures shown above, which were taken after this year's Kleeblattlauf, but they are the best I could find. My impression is that running is not among Andi's favorites, which probably explains his somewhat sceptical expression on the left picture. Fortunately, a few moment of recreation seem to brighten up things a little bit, as shown on the right. In any case, I wish Andi all the best for the future !!!

08.07.2014 : Morphing 

morphing14The not-newborn-yet-surprisingly-young generation to which I belong will recall the legendary Black or White video of Michael Jackson where faces of dfferent persons were morphed into each other for the first time. In a paper that has just been accepted for publication in Nano Letters we morph a metallic nanodisk into a nanotriangle, by producing particle shapes in between by means of electron beam lithography. One might call the description of this as morphing an exaggeration, yet it gave our paper a catchy title which is never wrong.

Why should one morph a nanodisk into a nanotriangle? In a series of recent papers [1,2] we have shown that the plasmon modes of a nanodisk can be characterized in terms of edge and film modes of different angular order. The idea, which was around for quite a while, was to morph the disk into different shapes to see how the modes of the disk evolve upon morphing. Our experiments and simulations indicate that the geometry modifications lead to energy shifts, splitting of degenerate plasmon modes, and to hybridization. Similar to the linear combination of atomic orbitals (LCAO) in quantum chemistry, we introduced a linear combination of plasmonic eigenmodes to describe plasmon modes in different geometries.

The paper has evolved in various steps. It started with the idea and first simulations that showed intriguing crossings of plasmon peaks. Next, Franz (our master of morphing) produced a number of metallic nanoparticles and the plasmon modes were analyzed in electron energy loss spectroscopy. Finally, we adapted a perturbation scheme for plasmon modes, which we had previously employed for rough plasmonic nanoparticles, to get an intuitive explanation for the evolution of the disk modes upon morphing. Altogether it was a fun collaboration with lot of feedback between experiment and theory. Nano Letters is one of the top journals in the field of plasmonics, and I am super happy that things worked out so smoothly. Many thanks to all collaborators!

27.06.2014 : Kleeblattlauf 2014

Kleeblattlauf 2014Kleeblattlauf 2014

On 27.06.2014 we had the annual relay race of our university, the so-called Kleeblattlauf, where four runners have to finish a course of 2.6 km / 2.2 km (female or 35+) below one hour. Despite the rather short distance, the course over the hilly terrain proves to be exhausting.

This year, our group started with three teams, namely #112 me, Magdalena Schreilechner, Andi Trügler, Robert Schütky, #113 Andreas Kleinbichler, Georg Jäger, Walter Pötz, Toni Hörl, and #114 Peter Senekowitsch, Daniel Lüftner, Daniel Kuppelwieser, Dario Knebl. As for me and my team, I am quite happy with our overall time of 0:46:37, in particular since we were the fastest of our teams.

27.06.2014 : Au@Ag nanocubes

NanocubeChemistry has been always magic to me. Partly this is due to my bad chemistry education, partly due to my arrogance in younger years when I thought that chemistry was inferior to physics. It took me many years to appreciate the magic and beauty of chemistry and to realize that it's natural sciences as such that attracts my interests.

In a paper that has just been accepted for publication in the Journal of Physical Chemistry, Luis Liz-Marzán and coworkers have chemically synthesized gold nanocubes exploiting seeding with silver nano spheres. Through magic, arguably through ligands attached to the gold surface, the nanoparticles arrange in beautiful arrangements, such as shown in the picture above, opening a wealth of interesting particle configurations. The surface plasmons of these nanoparticles have been analyzed in electron energy loss spectroscopy (EELS). Our contribution has been to supply the MNPBEM toolbox with the EELS extension. It was great to see how perfectly the simulations agree with experiment. I must admit that our contribution to the paper has been moderate, yet I am happy to be co-author of such a beautiful manuscript and I thank all coworkers for this pleasant collaboration.

17.06.2014 : Mag. Michael Reisecker

On 17.06.2014 Michi Reisecker passed his final exam. Michi has been with me for about a year, and his thesis (15 MB) deals with the simulation of silver nanodisks. In particular, we were interested in the question whether disk breathing modes, which we previously discovered in EELS, can be also detected in optical experiments. Indeed this is possible for oblique light incidence, and together with Markus Krug from the nanooptics group we performed a detailed experimental-theoretical study about this not-so-dark (darkish) breathing mode.

Although I have been super-happy with the Michi's performance, his true passion is mountaineering. Counting only the last year, Michi has skied through more powder and has climbed more routes than I have probably done in my whole lifetime. On our Glockner trip (see 11.03.2014) Michi embarassed us by skiing down under worst snow conditions with such ease, while we were literally creeping down the mountain. Needless to say that I cannot keep someone with such skills in my group ;-) In the next year Michi will try to start a training as a mountain guide, and I truly wish him all the best for that. Keep the passion alive!

11.06.2014 : It takes three

It takes three professors to promote the work of a single PhD student. At least this is what the image on the left suggests. In an article that has just appeared in our local university press about our recent Nature Communications paper, it is indeed this collaboration between Jo's nanooptics group, my theory group, and the electron microscopy group of Ferdinand Hofer that forms the grounding stone for our success.

Originally, the editor of the article, Gudrun Pichler, wanted to make a picture of ours where we act as we would in an experimental laboratory, but she soon realized that this was not a good idea. The present setting is more inspired by Manet's breakfast painting, but our talent for acting was rather moderate and we finally ended up with the above picture. So this is us, together with Hari Ditlbacher and Andreas Hohenau (not shown), who fight for the glory and success of our university.

14.04.2014 : Total reflexion

Usually I believe that physicists are good charcters, although I know a few exceptions to this rule. Yet, it is irritating to occasionally find odd statements of the grounding fathers of physics. Jo Krenn recently pointed me to an explanation (in German) of total internal reflection, given by the famous Arnold Sommerfeld, which is not particularly bad but uses a rather strange analogy:

Wenn es erlaubt ist, ein militaristisches Bild zu gebrauchen, so können wir die Sachlage folgendermaßen beschreiben: Eine geschlossene Armee stößt bei ihrem Vormarsch auf unwegsames Gelände, welches sie zwingt, ihre Marschrichtung zu ändern. Der Flügel der Armee detachiert eine schwache Patrouille mit dem Auftrag, parallel zur Grenze im unwegsamen Gebiet vorzudringen und die Flanke zu sichern. Diese Patrouille braucht in der Tiefe nur wenig Mann stark zu sein. Nachdem sie ihren Auftrag erfüllt hat, kehrt sie zur Armee zurück. So wie das Fehlen einer solchen Sicherung gegen alle Regeln der militärischen Vorsicht verstoßen würde, würde das unvermittelte Abbrechen unserer totalreflektierten Welle gegen alle Regeln der Elektrodynamik verstoßen.

And now for something completely different. The press release on our recent Nature paper (see 10.04.2014) made it into the Austrian newspapers. For some reason, press releases are usually in the form that person A says this and person B says that. Strangely enough it happens that I explain that there exists a simple equation which allows scaling between film and disk plasmon modes. I was now amused to see that in a newspaper article my explanation was further decorated by saying that it was given "with understatement". What am I supposed to say, maybe that we finally discoverd the equation-of-everything of plasmonics? By the way, the article ends by saying that our work might be beneficial for building future quantum computers.

10.04.2014 : The edge of glory

edgeElectron energy loss spectroscopy (EELS) has emerged as an ideal tool for the investigation of particle plasmons. An electron with a kinetic energy of 200 keV  passes by or penetrates through a metallic nanoparticle and excites surface plasmons. By analyzing the loss spectrum of the electron one obtains information about the surface plasmon energies, and by raster scanning the electron beam over the sample one can map out the plasmonic nearfields.

In the past we have investigated a "well-studied, almost archetypical, nanoplasmonic system -- a metallic nanodisk", as it was described by one of our referees, and have detected a new plasmon mode where electrons oscillate in the radial direction, which we called "breathing mode" in analogy to corresponding molecular vibrations (see news entry of 02.10.2012). In a paper that has just appeared in Nature Communications we now go back to the dawn of plasmonics and investigate surface plasmons in even more archetypical silver films and at the edges of these films. By confining the edges in the lateral direction, we were able to map out the plasmon dispersion of surface plasmon edge modes. Surprisingly, we found that the film and edge plasmon dispersions precisely coincide with the dispersions extracted for nanodisks. In the latter case, the circle of the disk boundary and the periodic boundary conditions along the circumferential direction, respectively, impose "quantization conditions" for the wavelengths of the film and edge plasmon modes. Such universal scaling comes as a true surprise, a remarkable finding that has been acknowledged by publication in the prestigious Nature Communications journal.

The work originates from a longstanding and successful collaboration between the nanooptics group of Jo Krenn, my group, and the FELMI group headed by Ferdinand Hofer. The true hero of the trade is again Franz Schmidt, hopefully becoming soon Dr. Franz Schmidt, who did a most careful job in obtaining and analyzing the EELS data. When it came to the interpretation of the results, I have experienced the nanooptics group as its best. Through all the years, Jo, Hari Ditlbacher and Andreas Hohenau have acquired an astonishing amount of understanding of surface plasmons, and it was fun to accompany them in the process of coming up with interpretations for the numerous EELS data.

The final key to our success is due to Jo Krenn, who succeeded to convince one of our rather critical referees. We thought that we could identify the person (although we were probably wrong), and through several weeks Jo used all his psychological skills to anticipate the assessment of the referee. Our final answer to him / her was a true masterpiece and worked immediately. Publication in the Nature journals will remain an exceptional feast for me, so I guess it is now time to celebrate. Thanks a lot to Jo, Franz, and all collaborators!

A press release in German can be found here.

08.04.2014 : Nie Mie

From 31.03.2014 till 09.04.2014 we had the pleasure of hosting Prof. Uwe Kreibig (RWTH Aachen) who gave a lecture series on "Optical properties of nanostructures". Kreibig is one of the plasmonics pioneers and has contributed to the forefront of this research field for about 50 years. He is author or co-author of numerous scientific papers and has written the book "Optical properties of metal clusters" that has become one of the standard references in plasmonics.

It has been great to see his persistent passion and enthusiasm for research in general, and recent developments in plasmonics, which has turned into a fashionable field within the last decade, in particular. Also the fundamental questions of "what is a plasmon?" and "when does a plasmon start to live and when does it end?" have remained a driving force for his curiosity. On the other hand, he is rather sceptical and critical about many recent developments, including quantum plasmonics, which has been investigated thoroughly already in the early years of plasmoncs (but seems to have become forgotten now). He has also kept a tempestuous relationship with Mie theory culminating in his famous list of the 25+ shortcomings of the theory.

Altogether it has been great for me and our students to experience the outstanding knowledge of one of the true heroes of the trade. Prof. Kreibig has also kindly provided us with the slides of his course, which can be downloaded as PDF monsters here, part1 (210 MB), part2 (190 MB). In any case, many thanks to Uwe Kreibig for visiting us and giving this exciting lecture series!

27.03.2014 : The rough side of plasmons (Part 2)

aufilmThe influence of surface roughness on the nearfield properties of plasmonic nanoparticles is the subject of a paper that has just been accepted for publication in Phys. Rev. B. Why should one care about such roughness? First, metallic nanoparticles that are produced through electron beam lithography are never mono crystalline but consist of metal grains, thus leading to surface roughness. Second, grain boundaries or other sharp edges or corners are hot spots for the plasmonic nearfield, where molecules can emit or scatter light extremely efficiently. This is for instance exploited in surface enhanced Raman spectroscopy (SERS), where the Raman cross section becomes boosted by many orders of magnitude.

In an older work of ours we have shown that surface roughness has practically no influence on the farfield optical properties. In this paper we now go one step further and investigate the nearfield properties, where things turn out to be much more difficult. The work was part of a FWF research project together with the nanooptics group (Andreas Hohenau) devoted to this topic, where we tried to understand the influence of roughness thoroughly but had to realize that things are considerably more complicated than we were expecting. Andi Trügler performed a huge number of simulations to disentangle the different contributions of changes of the dielectric function and of the particle geometry upon annealing of the metallic nanoparticles (in order to reduce the amount of surface roughness).

I think that the paper gives a nice resume of how we finally understand things. Before writing up the paper I had several moments of desperation, where I was completely lost in coming up with an intuitive picture for the different effects. In the several rounds of revising the manuscript I started to like the paper, and at least it has now given me confidence that whenever I will have to dig into the subject again I simply have to read the paper. Many thanks to all collaborators, in particular to Andi who worked extremely hard with the simulations. I guess it is not the most glorious of my papers, but it is a very sound analysis of a very hard topic and I hope that it will be appreciated by the plasmonics community.

11.03.2014 : Glockner in a day


We had planned an internal (and informal) group meeting on the Großglockner (3798 m) for a few weeks, but suffered some delay due to bad weather or difficult snow conditions. Finally we squeezed our trip in between two working days. On Monday the 10th of march, me, Toni Hörl, Michi Reisecker, and Andi Trügler left Graz in the late afternoon (a course of mine finished at 16:30) and drove to Kals where we arrived in the night. From 22:00 till 01:00 we went with our skies to the Stüdlhütte which had opened a few days before.

The next day we started our summit push around 07:00. The weather was extremely beautiful, with blue sky and almost no clouds, although it was rather windy and cold. Climbing the summit was easier than I had expected, but I owe a big thanks to Michi and Andi who were leading the final part. Skiing down was unfortunately rather exhausting, the snow conditions were moderate (as they have been throughout the winter). We arrived back in Kals around 15:00, jumping immediately into the car to be back in time for the lecture next morning.

Despite the tight time table it was a beautiful journey and a great experience. Contrary to what one might expect, we had practically no physics discussions but (nevertheless) a lot of fun. Thanks to Michi, Andi, and Toni for the great time.

14.01.2014 : On the cover of PCCP

PCCPA recent paper of ours just made it to the cover of  Physical Chemistry Chemical Physics (PCCP). It reports on a combined theoretical and experimental study which we performed in collaboration with the Kautek group (TU Vienna). The main idea is to use femtosecond laser pulses in combination with scanning near field tips for controlled nanolithography. This is achieved by exploiting the huge plasmonic nearfield enhancements at the tip.

The true heros of the trade are Christian Huber (TU Vienna) and Andi Trügler who worked hard to understand the details underlying such nano lithography. One particularly nasty problem concerned the modelling of the tip, which we approximated in our MNPBEM simulations as a nanoparticle of finite size. Replacing the extended tip structure by a finite nanoparticle lead to a series of particle-like plasmon resonances, and we had a hard time to disentangle the effects of these particle-like resonances from those of the geometric factors (tip sharpness etc.) which we were particularly interested in.

The final paper is a fine piece of work and presents a systematic study of femtosecond nano lithography. At the end the editors asked for an artwork graphics that could go to the front cover of the journal, and Andi spent a few days to finally come up with the above illustration. Thanks to him and all collaborators for this pleasant collaboration!

18.11.2013 : Signs from the past

IxtlanWhile my climbing activities have drastically dropped in recent years, several other group members keep pushing their rock limits with great success. A few days ago Michi Reisecker, who is in the shape of his life, and Andi Trügler sent the legendary and expo route "Reise nach Ixtlan" in the Bärenschützklamm (congratulations !). On this occasion, they discovered an old signature of mine proving that I was there in the glory and stronger days of my youth. I must confess that it was my partner Heli Renger who was leading most of the pitches, nevertheless I recall that I was extremely happy and proud having climbed this route.

16.11.2013 : Dance your PhD

For several years I was suggesting dance performances of research fields as a compulsory part of applications for employment, but of course this was never implemented. One might wonder whether the few moments of joy (rather for the audiance than the candidate) would be worth the long period of revenge from the successful candidate, but this is a different topic.

Recently, I stepped over a "Dance your PhD" competition for students, who seem to find such a performance not humiliating at all but rather joyful. Personally, I recommend watching the generation and manipulation of multiphoton quantum states but also the more down-to-earth topic of sperm competition between brothers and female choice. Maybe we should start thinking about our own plasmonics dance?

07.10.2013 : MNPBEM13 logo

MNPBEM13 logoFinally, our MNPBEM toolbox has its own dignified logo. It is a SEM picture of gold nanoletters, which have been produced with electron beam lithography. We cordially acknowledge Christine Prietl of the nanooptics group for the fabrication. I like the idea that the toolbox is designed for the simulation of metallic nanoparticles (in particular of plasmonic resonances), but in turn uses an "experimental" logo.

PS: There have been complaints from qualified colleagues that the above letters are not really state of the art. I must admit that we have also received more perfect images. However, I like the fringy letters because they nicely show the imperfections of electron-beam lithography and give us a short break from the shiny-perfect illusions usually produced from simulations.

04.10.2013 : MNPBEM13

A new version MNPBEM13 of our toolbox for the simulation of plasmonic nanoparticles is now available for download. The new version corrects a few minor bugs and inconsistencies of the previous toolbox. The full version of the MNPBEM13 toolbox will include two classes for the simulation of electron energy loss spectroscopy of plasmonic nanoparticles. Stay tuned for more.

22.09.2013 : Matlab toolbox OCTBEC

octbec13Optimal control theory (OCT) is a mathematical device which allows to optimize dynamic processes that can be controlled by some external control parameters, in order to fulfill certain control objectives. A typical example is femtochemistry, where a femtosecond laser pulse is shaped such that molecules are brought from some initial state to a desired final state. We were introduced to the field of OCT more that 10 years ago by Alfio Borzí, who was working at the Institute of Mathematics in Graz at that time. After a while we realized that an ideal physical system for the implementation of OCT are ultacold atoms and Bose-Einstein condensates (BECs) in atom chips, where the condensate wavefunction is controlled by the magnetic fields produced by the atom chip. In turn, we established an extremely fruitful and pleasant collaboration with the Schmiedmayer group at the Atominstitut in Vienna (see numerous older new entries).

From a physics point of view, OCT often appears as magic. An example is shown in the image above, where a condensate wavefunction is transferred from the ground to the first excited state of an anharmonic trap by simply displacing the trap minimum. Even for a lousy initial guess for the displacement protocol, OCT comes up after a few iterations with an almost perfect scheme.

In a paper, which has now been accepted for publication in Computer Physics Communications, I have now published our simulation programs that are put together within the Matlab toolbox OCTBEC. The toolbox provides a variety of Matlab classes for simulations based on the Gross-Pitaevskii equation, the multi-configurational Hartree method for bosons, and on generic few-mode models, as well as optimization problems.  These classes can be easily combined, which has the advantage that one can adapt the simulation programs flexibly for various applications.

I owe a big thank to those who have contributed to the development of the software. Alfio Borzí and Greg von Winckel have helped a lot in setting up the methodology at the beginning of our work. Julian Grond has worked hard during his PhD thesis to push OCT of Bose-Einstein condensates to the extreme, and has successfully established OCT for fragmented and excited condensates. I hope that the toolbox will be useful to a broad community interested in optimization and control of BECs.

29.08.2013 : Smooth as a filter  

At the end of november 2012 Georg Jäger passed his final master exam (see older news section). His thesis was devoted to optimal quantum control simulations of Bose-Einstein condensates in magnetic microtraps, where the control becomes distorted by a filter, as is often the case in experiments. Soon after Georg started his PhD work, and the master work went into my production line for publication. Unfortunately something blocked the line, to come up with a lame excuse, and I delayed the writing again and again.

In the beginning of July, when summer term ended, I finally found time to start clearing the line. While writing the manuscript, I realized what a great job Georg had done with his thesis. The paper had a smooth refereeing process and has now been accepted for publication as a brief report in Physical Review A.

23.08.2013 : Dot meets wire  (PDF)
nanowire.jpgControlled coupling between single or few quantum dots and a silver nanowire is demonstrated in a paper that has just been accepted for publication in Nano Letters. The structure is fabricated in a two-step lithography process developed by the nanooptics group, where quantum dots and nanowire are positioned consecutively by using electron-beam lithography. In the experiments the quantum dots are excited off-resonantly, and subsequently decay into surface plasmons propagating along the wire which finally decay readiatively at the wire ends. By monitoring the spectrally or temporally  resolved luminescence, one obtains detailed information about the composite dot-wire structure.

The experiments were performed by Christian Gruber as part of his PhD work. I remember that Christian showed me his results about one year ago at the NFO meeting in San Sebastian (it seems that we often talk more to each other when we are on conferences, although we work in the same building), and the results showed a mix of expected and surprising features. In the following I devised a simple and generic few-level scheme, which I had used in the past for describing quantum dot physics and which usually performs extremely well despite its simplicity, and indeed several features could be well explained while others remained still unclear. The rest of the story turned out to be more tedious.

First, Andi Trügler performed a huge number of simulations in order to understand how the quantum dots couple to the plasmonic nanowire. These results could explain many things, yet the uncertainty of the precise number of dots and of their dipole orientations, as well as blinking effects made a direct quantitative comparison very difficult. Writing up the manuscript was complicated by the fact that Jo Krenn, who is currently head of our institute, was overloaded with bureaucratic burdens, although he finally managed (as always) to compile things in an excellent manner. During writing we started to understand several pieces of the physics involved more deeply, but whenever we added one piece of understanding to the puzzle other questions emerged.

I think that the final manuscript gives a clear picture of the physics underlying the coupled dot-nanowire system and makes huge progress in comparison to previous studies. Yet, it points into several directions for future research. Altogether, I like the paper a lot and I hope that it will be appreciated by the scientific community. Special thanks go to Christian and Andi, who did a great job with the experiments and simulatons and who were extremely patient in revising the figures again and again, as well as to Jo who finally managed to defeat his desperation in the write-up process and to come up with a final masterpiece.

30.07.2013 : Tomography of plasmon fields  

Visualization of scientific results has always fascinated me, starting from the early days of my diploma thesis when I was using programs like erlgraph (an ancient graphics toolbox developed in Erlangen) or the software tools developed by Silicon Graphics. In the following years I became particularly attracted by experiments that provide a clear and direct image of the nanoworld, such as the atom chip experiments of the Schmiedmayer group, which allow the visualization of many-body wavefunctions, or electron energy loss spectroscopy (EELS) of plasmonic nanoparticles, which visualize the electromagnetic fields of surface plasmons.

In a paper that has just been accepted for publication in Physical Review Letters, we now go one step further and demonstrate how EELS can be used to extract, within a tomography scheme, a full three-dimensional map of the plasmon fields. Electron microscopy has emerged as the ideal camera for the nanoworld, as it combines sub-nanometer resolution with high spectral resolution. In our paper we show that a collection of rotated EELS maps allows to reconstruct the 3d plasmon fields, using a tomography scheme (Radon transformation) that is commonly employed in computer tomography. The topic is hot and experiments are under way, so I hope that our work will prove useful to the community.

The work has a relatively long history, Andi Trügler and I have been thinking quite a while how such a reconstruction could work. It was finally Toni Hörl, who recently started his PhD thesis within the SFB NextLite, who took over the work and brought it to a positive end. I think that there is still plenty of room for improvements and extensions, nevertheless I am super-happy that the paper is now through and I am looking forward to applying our scheme to real experimental data.

30.07.2013 : Late greetings from Jyväskylä

Back in 2011, Jussi Toppari invited me to a summer school in Jyväskylä, Finland, where I spent one week in an extremely friendly and pleasant atmosphere, enjoying also the traditional Finish Sauna in the long August evenings. During and after the summer school we developed a joint research plan, which was devoted to strongly coupled modes between surface plamons and molecules. Whether these modes should be called plexcitions or not remains disputed, even among our referees.

Although I found the work very nice and convincing, we had a hard time to get the paper through. Usuallly refereeing helps to improve the quality of a paper, and this is also true for this work, nevertheless it is often hard to simultaneously please all reviewers. I am very happy that our paper has now been finally accepted for publication in Physical Review B, and I would like to thank Jussi for starting this collaboration -- and pushing it through till the glory end.

25.07.2013 : wiki-based labbook

Documentation of scientific results has always been a weak point in my career. With the exception of handwritten notes, which I have collected in folders, only very few notes about our work in progress have survived through the years. Redoing things that have worked in the past but which have become forgotten in time is tedious and annoying, and I have always jealously observed experimental physicists who have grown up with labbooks and are able to recall things from the past so easily.

Things have changed now. Andi Trügler has set up a dokuwiki page that allows me and all group members to provide a documentation of what we are doing, and to collect our results and thoughts about future plans in a very convenient form. Within the first months things have worked out well, and we are now looking into a hopefully well-documented future.

04.06.2013 : Mag.a
Miriam Mutici

On June 4th Miriam Mutici passed her final exams with distinction. Miriam's diploma thesis has been devoted to the theoretical desription of quasi one-dimensional Bose-Einstein condensates, in particular in connection with the question of how to use density matrix hierarchies for the description of condensate fragmentation and twin-beam creation. Things turned out to be somewhat difficult, and we compared and tried a number of different approaches in order to get a better understanding of the underlying physics. A detailed account of her work can be found in her diploma thesis.

With hindsight the outcome of the work was less obvious and clear as I was initially hoping. Nevertheless Miriam did a great job and pushed things as far as possible. I wish her all the best for the future, whatever she will decide to go for.

14.05.2013 : 20th anniversary of quantum state engineering

quantum state engineeringAn article on optimal control theory of Bose-Einstein condensates (BECs) just appeared in the special issue of the Journal of Physics B on the "20th anniversary on quantum state engineering", edited by Rainer Blatt, Gerard J Milburn and Alex Lvovksy. The paper comes together with a LabTalk that gives some background information about our joint experimental and theoretical work, which demonstrates that BECs can be controlled with extremely high fidelity in atom chips. Thanks to all collaborators, in particular to Robert Bücker from the Schmiedmayer group who pushed the analysis to the extreme. Enjoy reading.

03.04.2013 : Mag. Robert Schütky

Today Robert Schütky finished his final diploma exam with distinction. Robert's thesis, which was supervised by me and Christian Ertler, deals with surface plasmons in topological insulators. The topic was suggested by Christian, an expert in spin physics, who recently started to work with topological insulators. A number of papers deal with this subject and indicate a rich physics, so we decided that it was time to find out whether we could add something new to this field.

Unfortunately many of the steps involved in the analysis proved more difficult than we initially thought. In particular the calculation of the 2D dielectric function for Dirac fermions turned out to be rather complicated, and although we followed two scientific papers we were often puzzled by the "straightforward calculation" and "simple steps" that led to the final results.

Robert demonstrated an enormous patience and resistance, and passed all steps with flying colors. He finally even mastered the tricky navigation of Mathematica through the complex plane without getting lost  on the different Riemann sheets. Unfortunately, at the end it turned out that the effect we were chasing after was much smaller than we were hoping. Nevertheless, Robert delivered a fine piece of work and deserves a lot of respect for this. He will now continue as a PhD student and I am looking forward to the collaboration to come.

03.04.2013 : Next Lite

NextLiteLast month the SFB Next Lite, which is funded by the Austrian science fund FWF in the years 2013-2017, started. A press release (in German) has now been published on the website of our university. The SFB has been initiated by Gottfried Strasser from the TU Vienna, and already the pre-stage of the project has been a true pleasure. With "start your engines, gentlemen" Gottfried informed us about the acceptance of the pre-proposal, and now with "Mander s'isch Zeit" he made clear that things are ready to start -- I am looking forward to a successful and pleasant cooperation in the next years.

19.03.2013 : Mag. Jakob Ebner

After more than a year of hard work, Jakob Ebner finished his final diploma exam with distinction. Jakob's thesis has been devoted to the theoretical description of the optical properties of hybrid semiconductor-metal nanoparticles, where the excitonic response of the semiconductor becomes amplified by the metallic nanoparticle. The main challenge of the work was to figure out how the different Coulomb couplings need to be screened, and how to properly account for the electrodynamic response within a quantum-mechanical description scheme.

Things turned out to be more complicated than we initially thought, and Jakob had a hard time to develop both the methodology and the numerical simulation of the problem. I think that Jakob did a great job and showed enough passion and patience to finally bring everything to an end. A publication in a journal will follow hopefully soon.

Fortunately, both Jakob as well as Toni Hörl will continue as PhD students in my group within the SFB project Next Lite. So there is still enough to come from both of them, and I am lookling forward to continuing the pleasant collaboration.

23.01.2013 : Hot electrons from plasmonic nanoparticles

hotelectron.jpgMetallic nanoparticles sustain coherent electron charge oscillations at the interface between the metal and the surrounding dielectric (air), so-called surface plasmons, which lead to extremely strong and localized "evanescent" fields in the vicinity of the nanoparticle. When irradiated with a femtosecond laser pulse, the electric fields can be so strong that electrons become liberated from the metal, either through multiphoton absorption or through quantum mechanical tunneling, and are subsequently accelerated by the same evanescent fields. In a paper, that just has been accepted for publication in Nano Letters, we demonstrate such emitters of ultrafast electrons with kinetic energies of several tens of eV's experimentally, and reveal through supplementary simulations the details underlying the emission and pondetomotive acceleration processes.

The work is a collaboration between three groups, namely Peter Dombi from Budapest who performed the femtosecond optical experiments, the nanooptics group of Jo Krenn contributing the nanoparticle samples, and my group simulating the experimental results. Throughout the collaboration has been a true pleasure. From the simulation side, Toni Hörl is the person who has contributed most, and an appraisal for his work has already been given in the previous news entry.

The paper has seen an extremely long and difficult refereeing process, and I must say that I have probably never spent so much time with a single manuscript. I am happy that we finally managed to embark the paper in the prestigious Nano Letters journals. Our work leaves a number of logical follow-up experiments and I am looking forward to continuing this challenging and emerging field of reserach. Thanks a lot to all collaborators!

29.11.2012 : New masters

This week two of my former Master students passed their final exams. First came Toni Hörl on tuesday. His master thesis was devoted to the simulation of ultrafast electron emission from plasmonic nanoparticles, a study that we did in cooperation with the groups of Jo Krenn and Peter Dombi (Budapest). In the experiments a femtosecond laser pulse liberates electrons from the metal, either through multiphoton absorption or through tunneling, and the electrons become accelerated in the strong, evanescent fields of the plasmonic nanoparticle up to kinetic energies of several tens of electron volts.

In the beginning we made quick progress and could reproduce the energies of the fastest electrons quite easily. Understanding the details of the emission process and the spectral distribution of the emitted electrons turned out to be a true challenge, and Toni proved to be the ideal partner for facing this challenge. Toni is a modest person and in the beginning I had a hard time figuring out whether he understood the explanations I was giving to him, as there was no clear response from his side. However, I soon realized that he understood perfectly well and that he simply needed time to digest things, and to finally come up with new, often rather unusual suggestions or solution schemes. I am very happy with the work he finally delivered and the paper we wrote, which is still under review. The most impressive thing about Toni is certainly his way of storing things, both on his desk and computer. Being myself a rather unorganized person, I still found his approach completely chaotic, although Toni never had problems in immedialtely finding things.

The second new master is Georg Jäger who had his exam one day later. His thesis is devoted to optimal quantum control of Bose Einstein condensates. Experiments for shaking up Bose Einstein condensates in the magnetic microtrap of atom chips have previously been carried out by the group of Jörg Schmiedmayer (TU Vienna). In the experiments they were using excitation protocols designed with optimal control theory, which turned out to work perfectly well. One problem is often the time response of the electronics, which acts as kind of filter that distorts the input control.

In his work, Georg devised a scheme for implememting this filter response properly within our optimal control approach. Georg had a hard time keeping our activities in the field of BECs alive, while most other work was shifting in the direction of plasmonics. Nevertheless, he did a great job and finally pushed the shakeup scheme to the limits, suggesting protocols that could perform extremely fast. Throughout I was amazed by Georg's handwriting and his ability to fill the blackboard with a single equation.

Congratulations to Toni and Georg for their performance and for finally becoming a Master of Science, and thanks a lot for the wonderful time I could share with them.

20.11.2012 : Prize for Andi Trügler

Congratulations to Andi Trügler for receiving the prize for simulation and modelling of the province Styria (Forschungspreis des Landes Steiermark für Simulation und Mdellierung, Kategorie Nachwuchsförderung). The prize was awarded for Andi's outstanding PhD thesis, a detailed introduction into the field of plasmonics and simulation of plasmonic nanoparticles, which also contains the about ten papers published in international journals. Andi is a true master of his discipline, and I am proud and happy that he now also receives the recognition that he certainly deserves for his work.  Congratulations again!

12.11.2012 : The future of plasmonics (and different things)

Jo KrennObama

Congaratulations to Jo Krenn who was invited to give a two-page interview about the perspective on plamonics in the most prestigious journal Nature Photonics. Jo started his research career in Graz in the group of Franz Aussenegg, one of the early pioneers in the field of plasmonics, and has since then remained at the forefront of this field that has become tremendously active within the last decade. In the interview Jo proves to be a true statesman by giving fair credit to all pioneers of the field, including the Austrian-Hungarian scientist Richard Zsigmondy, who used in the 1920's an ultramicroscope to observe single metallic nanoparticles. Enjoy reading the interview.

Talking about statesmen, last week saw the fortunate reelection of a gentleman shown on the right picture together with our witness of marriage, Mark Gillespie, a professional photographer from Michigan who made a shooting of Obama during his first campaign back in 2008. I hope that the second half of his presidentship will shine as brightly as the (yet to come) future of plasmonics!

09.10.2012 : Serge Haroche

Today Serge Haroche received (together with David Windeland) the Nobel prize for his beautiful work demonstrating the controlled manipulation and measurement of few or single photons inside of superconducting cavities. What might be less known (and will probably become forgotten in the annals of physics) is that in the years around 2006 I published two papers in PRL and PRA where we investigated decoherence of atoms trapped in the vicinity of superconducting atom chips. These papers have a remarkable history in their own right, and would have certainly made it into my news section if it had existed at that time. Today I am happy to announce that both papers were cited a few times by Haroche and coworkers. Being cited by a Nobel laureate has no implications whatsoever and does not ennoble my manuscripts, nevertheless it is something nice that I wanted to share with you in this news section.

02.10.2012 : Dark plasmonic breathing mode

EELSFinally summer break is over and I am back with good news: a paper of ours on "Dark plasmonic breathing mode in silver nanodisks" was just accepted for publication in Nano Letters. How comes that we ended up on the dark side of the otherwise so brightly shining surface plasmons? Surface  plasmons are collective electron oscillations at the interface of a metal and a dielectric that come together with strong and evanescent electromagnetic fields, that allow to confine light to the nanoscale.

Typically only a few of these surface plasmons have a net dipole moment and couple to light, the others appear dark. Yet, these dark plasmons are important for properly describing plasmon-molecule couplings or plasmon hybridization. In recent years, electron energy loss spectroscopy (EELS) has emerged as an ideal tool to monitor both bright and dark plasmons with nanometer resolution. In EELS an electron beam passes by the metallic nanoparticle, excites a surface plasmon and loses energy. By analyzing the energy losses one obtains a map of the surface-plasmon field distribution.

Our new paper reports results of a collaboration between the nanooptics group of Jo Krenn, the FELMI center at the TU Graz headed by Ferdinand Hofer, and myself. The true hero of the trade is Franz Schmidt, who spent hours at the electron microscope mapping out the plasmon modes of silver nanodisks. Surprisingly, we observed for this simple "archetypical, nanoplasmonic system" (as it was called by one of the referees) a new plasmon mode associated with oscillations in the radial direction, which we termed in analogy to molecular systems as a "breathing mode".  This mode does not couple to light and has therefore escaped optical detection. Yet, it might impact the hybridization in coupled nanoparticles as well as couplings with nearby quantum emitters. As a historical side remark, the symmetry properties of this mode were first foreseen by Hari Ditlbacher, an experienced plasmon warrior of the nanooptics group, and it took me a few simulation attempts to finally support this point. Congratulations to everyone -- and keep on looking closely at the nanoscale, it seems that there are always surprises around.
22.06.2012 : Kleeblattlauf 2012

University used to be a quiet little place. We were teaching a number of courses, and the remaining time was devoted to research. Things have considerably changed in recent years. First came the "performance record", a database that puts the performance of our scientific output and activities into the measurable quantity of a mere number. Next came an electronic system for teaching, uni-graz online, a highly complex database that is now ruling university.

Now it hit the final terrain of freedom, the Kleeblattlauf, a relay race of the university that has to be finished by four runners within one hour. For all the years we survived without a time-keeping system. Time was measured generously in order to fulfill certain requirements, such as being faster than other groups (in our case the theoretical particle physicists). Paradise has finally come to an end. Starting this year there is now an official time keeping by zeitnehmung.at.

So from now on I will simply stay with the bare facts. The solid state group started with three teams, (#102) me, Miriam Mutici, Toni Hörl, and Jakob Ebner, (#104) Rene Hammer, Georg Jäger, Walter Pötz, and Christian Ertler, as well as (#106) Matus Miklo, Daniel Lüftner, Daniel Scheiber, and Andrei Reyes Huamantinco from Leoben. As for me, I opted again for the shorter "senior" distance of 2200 meters, which I finished in 08:50, and altogether the group needed 00:47:18. Besides these mere facts, the race was fun and we enjoyed afterwards the beautiful evening with one or two beers. Congratulations and thanks to everyone.

22.06.2012 : Teaching electrodynamics

There has been a lot of work but no news recently. Among many other things, I have been involved in setting up a new bachelor curriculum (together with the TU Graz) and teaching a course in electrodynamics. In preparing the lectures I stepped over a beautiful letter from Farady to Maxwell, where he is complayning about too formal routes towards physics:

When a mathematician engaged in investigating physical actions and results has arrived at his own conclusions, may they not be expressed in common language as fully, clearly, and definitely as in mathematical formulae? If so, would it not be a great boon to such as well to express them so -- translating them out of their hieroglyphics that we might also work upon them by experiment?

In the final part of the course, when I was teaching the relativistic formulation of electrodynamics, I also had to realize (with desperation)  that virtually all text books refrain from an intuitive interpretation of the formalism. An article on "Application-oriented relativistic electrodynamics" seemed to promise help, in particular since the focus was on teaching relativistic electrodynamics, but already in the abstract the author makes clear that

What emerges as general guidelines are the facts that Relativistic Electrodynamics should be presented axiomatically, without trying to “explain the physical meaning” of Special Relativity, that four-vectors and their mathematical properties should be emphasized, and that the field tensors, an elegant formalism, albeit of limited practical use, should be avoided.

If, accidentally, someone is stepping over a simple explanation of the topic, including a way to visualize the derivative of four-vectors in such intuitive terms as the divergence and curl, please let me know. Otherwise I have to give in to the axiomatic approach.

24.03.2012 : Twin atoms reloaded   (PDF)

twins12Last year we published together with the Schmiedmayer group a paper on the creation of twin atoms from a one-dimensional degenerate Bose gas. At that time our task was to design an optimal control ramp for bringing the condensate into a (transversally) excited state, although the main point of the work was the ensuing relaxation process where two atoms in the excited state decay via a two-body process into paired, propagating modes with identical population and opposite momenta (twin atoms).

In late 2010, when we were close to submission of our first paper, I attended a rather boring workshop in Vienna and I skipped the last afternoon session to meet with the atomchip group and to discuss (with great excitement) the physics involved in twin atom creation. Later in the evening I returned with Julian, who at that time was working at the Atominstitut, to Graz, and I remember that in the train I first realized that with our experience in the field of atom interferometry we should be able to describe the process of twin atom production (at least in principle). The next day I started to work on the problem and devised a simple two-mode model whose results were in surprisingly good agreement with experiment.

As always in the collaborations with Jörg and his group, this was the beginning of a long (but pleasant) story. It soon turned out that it was necessary to change to a density matrix description to cope with more modes and to include many additional features relevant for the experiment, and I soon began to realize that I was running into a kind of endless story. At some point Robert took over with the simulations. It may be due to his youth, his strong faith in the strength of our model (as theoreticians we seem to be more attracted by the weak points), or simply the larger amount of time he was investing, in any case, it was amazing to see to which level of perfection he was pushing the agreement between experiment and theory. It is fair to say that Robert is the true hero of this work, considering also the mere 35 iterations it took to bring the paper to its final form. I think that we finally succeeded to compile a beautiful piece of work. Thanks a lot to all collaborators!

19.03.2012 : Hungarian evergreen    (PDF)

Back in 2003, when virtually every system was considered as a viable candidate for quantum computation, we published a PRL about STIRAP-based quantum gates, building upon a beautiful proposal of Kis and Renzoni. Later in the same year I met Zsolt Kis in Kaiserslautern, where he was working at that time and where I gave a talk.

In 2008, several years later, Zsolt suggested to apply for a bilateral project between Austria and Hungary, together with Gabor Demeter and Gagik Djotyan. The summer of the next year brought me for the first time in my life to Budapest, a beautiful city with a lot of history, and I was enjoying the hospitality of Zsolt and Gabor. From a physics point of view my stay was successful, and we figured out a number of topics for possible collaborations.

In what followed Zsolt, Gabor, and Gagik visited me twice in Graz. We had a lot of discussions and our collaboration made significant progress, mainly due to Gabor and Zsolt. I feel a littly guilty that I was not contributing more, but, honestly speaking, I was completely stuck with other things. We finally submitted a beautiful piece of work, which had the smoothest refereeing process I have ever seen. The referee was extremely polite and concluded that "This is a very well written paper on pulse propagation in a multi-resonant medium. The field of pulse propagation, although perhaps not in the forefront of current theoretical and experimental interest, is an evergreen". So thanks a lot to Gabor, Zsolt, as well as to the unknown referee!

22.02.2012 :
Totes Gebirge

Totes Gebirge

Crossing the Tote Gebirge with skis has been on my wish list for several years. The Tote Gebirge is located between the provinces Styria and Oberösterreich, and is one of the most remote areas in Austria. It typically takes two to three days to cross the entire region.

In the last years my son Moritz and me had tried (and failed) twice: in 2010 we started too late and finally had to return to our starting point at the Loser in Altausee, in 2011 we gave up because of foggy conditions. This year we were lucky with the weather, the forecast promised two sunny days, and we started early enough to reach the Applehaus early in the afternoon where we spent a cold night in the winter room.

On the next day we finished our tour-de-force with a 11 hour walk, passing through one of the most beautiful and lonesome regions I have ever seen. I owe a big thank to Moritz, who was pushing me and who was bravely leading the final part of our tour. In the last glimpse of the sunlight we arrived at our final destination Tauplitz. 

27.01.2012 :
Solid state skiing 

solid state skiingsolid state skiing 2

On friday our solid state group, which is partially more condensed than solid, went for a ski day to the Präbichel. The weather and snow conditions were perfect, and we had a lot of fun and surprisingly little physics discussions. The picture above shows (from left to right): Jürgen Waxenegger, Jakob Ebner, Robert Schütky, me, Andi Trügler, Rene Hammer, Georg Jäger, Miriam Mutici, and Christian Ertler (middle on right picture, photographer of the left picture). It is good to see that there are other great things in life except of physics ...

24.01.2012 : Third harmonic generation  

THGIn a nonlinear optical process light interacts with matter and a photon is transformed into several photons of lower frequency (energy), or, in a reversed process, several photons are transformed into one photon of higher frequency. Third harmonic generation (THG) describes the process where three low-energy photons generate, in presence of a polarizable medium, one high-energy photon. In a work, which just has been accepted for publication in Nano Letters, we demonstrate that such conversion is significantly enhanced for metallic nanoantennas, where surface plasmons can be excited and the nonlinear process becomes boosted by the strongly localized plasmon fields.

About two years ago we started to perform simulations for experiments that were performed by Tobi Hanke in the group of Alfred Leitenstorfer and Rudi Bratschitsch. I know both Alfred and Rudi from the very early days of my physics career, when all of us were working in the field of coherent semiconductor optics, and it was a great experience collaborating again on a new topic. Andi Trügler spent a huge amount of time with the simulations, which were challenging both from the computational and methodology point of view. On the one hand, our MNPBEM toolbox is not optimal for large particles (since we are currently using a pure collocation method), while on the other hand it turned out to be necessary to model the full coherent THG emission process.

At the end we could deliver a message that is as simple as a message can be: the amount of emitted THG radiation is directly linked to the dephasing properties of the nanoantennas -- the smaller the dephasing, the larger the THG intensity. I think that the final manuscript describes a beautiful piece of work. The collaboration was longish but nevertheless most rewarding, including both physics as well as a beautiful ski tour (Preber) together with Tobi at the Mauterndorf winter school. So thanks a lot to everybody!

18.01.2012 : Most downloaded

Our MNPBEM Toolbox made it into the selection of the most downloaded Computer Physics Communications articles. We hope that people come along well with the programs and enjoy the toolbox!

For 2012 we plan a few improvements. First, we would like to add a more user-friendly interface where the different options and simulation modes (static and retarded) can be set via a single mnpbemset function, similar to the odeset function of the ODE Matlab solver. Second, we will add plot functions for compstruct objects (such as sig). Most importantly, we will implement an interpolation of the curved particle boundaries, using shape functions for the triangles and quadrilaterals. With this, the closed argument of the comparticle objects will become obsolete and the Green functions can be integrated more accurately over the face elements, which should be beneficial for larger nanoparticles.

So these are our plans, not very much has been done so far.  In any case, stay tuned -- we hope to have something ready in the second half of 2012.

18.11.2011 : Mag. Christof Weber

Last friday Christof Weber passed the final exam of his diploma studies.  Christof's thesis deals with electron energy loss spectroscopy (EELS) and microscopy of plasmonic nanoparticles, in particular for situations where the electron beam passes through the nanoparticle. The critical thing is how to describe within our boundary element method (BEM) approach the crossing point of the electron beam with the nanoparticle boundary, as one has to be rather careful in dealing with the diverging potentials and fields close to the beam. To be sure that things are done properly we decided to compare the results with Mie theory where analytic solutions are available.

Christof succeeded half way and obtained reasonable agreement between the BEM and analytic results. Yet, it appears that more work is needed to properly implement EELS into our MNPBEM toolbox. Nevertheless, at some point it was time for Christof to write up things and finish. I wish him all the best whatever his future will bring.

26.09.2011 : MNPBEM Toolbox published

A paper describing our MNPBEM toolbox for the simulation of plasmonic nanoparticles, as well as the program files, have been accepted for publication in Computer Physics Communications, and can now be downloaded here. We ask all users to cite the Comp. Phys. Commun. paper.

There exists also an extended version of the toolbox, which includes symmetry and layer structures, whose download requires a password. These additional features are still somewhat experimental and under development.

23.08 - 01.09.2011 : Bike tour through the dolomites


From 23.08 – 01.09.2011 me and my son Moritz, now 16 years old, were biking through the Dolomites and the mountains close to the Swiss border. After our tours Austria–Paris (2009) and Swiss mountains (2010), this was our third tour in a row. Again we were extremely lucky with the weather (hot and sunny, with the exception of two rainy days), and we climbed in ten days approximately 17000 hm. Highlights were the beautiful Sella round, the Passo Giau and the Stilfserjoch, just to name a few. Altogether it was a beautiful experience, exhaustive but in many ways rewarding. A more detailed tour description (in german) can be found here.

01.08.2011 : Prime numbers

Just in case someone is interested: 2011 is the 305th prime number (the next one is 2017). You can check this in Matlab with primes(2011).

20.07.2011 : Dr. Andreas Trügler

Andi TrüglerAfter 3 years of PhD work, today Andi Trügler passed his final Rigorosum exam with distinction. Within the last few years Andi has been the key person and backbone for the plasmonics activities of my research group. He has successfully handled a large number of projects, mostly with experimental groups, and I think that the output of his thesis of about ten papers is quite remarkable.

Andi is a relaxed person (with the only exception of the last days before his final exam) who does his work quietly but with great care. Through all the years we have worked together I have been fully satisfied with his performance and output, and I am sure that Andi will make his way whatever he approaches in the future. The original plan was that he would continue a Postdoc for another two years,  but since the project for which we applied was not funded in the first round we now have to improvise, and I hope that we will find a solution. In any case, the next few weeks Andi will travel through the Suisse mountains, relaxing from physics and hopefully being stressed by other things.

17.06.2011 : Kleeblattlauf 2011

Last friday it was time again for the yearly Kleeblattlauf, a relay race organized by our university that has to be finished within one hour. The solid state group started with two teams, namely me, Christof Weber, Jürgen Waxenegger, and Miriam Mutici (team #158) and Peter Senekowitsch, Christian Ertler, Rene Hammer, and Walter Pötz (team #160). As regarding my performance, I was suffering from a complete lack of running workout and thus opted for the shorter distance, which gave me at least the great feeling of finishing the course among the first. At the end, both teams were equally strong, and the final runners came in simultaneously after about 50 minutes. Congratulations to everyone!

17.05.2011 : Measuring a quantum-mechanical wavefunction   (PDF)

Measuring a quantum-mechanical wavefunction is a popular and not so difficult Gedanken experiment in quantum mechanics, but to actually measure it in experiment remains a hard endeavor. In the past, my interest as a theoretical physicist has been somewhere in between: we have suggested and analyzed experiments that could do the job. A technique of particular interest is scanning nearfield optical microscopy (SNOM). Here light is quenched through the tip of an optical fiber, which allows to probe optical excitations in semiconductors (excitons) with nanometer resolution, and opens the possibility to map out the exciton wavefunction.

In a recent work, that is based on the diploma thesis of Jürgen Waxenegger and which has now been accepted for publication in Physical Review B, we extended the analysis to the mapping of excitons in carbon nanotubes with a metallic nanosphere using a so-called apertureless SNOM setup. This approach appears to be quite feasible in experiment, at least this is how it seems from a theoretician's perspective. Although we initially advertised our work as a "wavefunction mapping" in carbon nanotubes, a referee rightly pointed out that the simulated experiment rather gives information about the coupled exciton-nanosphere system than the exciton wavefunction itself, so we finally weakened our claims. In any case, we hope that our work will stimulate further experiments in this direction.

13.05.2011 : All good things come to an end

At the beginning of my career it happened once that a paper of mine did not make it through the refereeing process. It was not that the referee reports were particularly bad, rather I felt disappointed that the work, which I considered to be fine work, did not receive the perception I was expecting, and I never re-submitted. Later I realized that this was a mistake, but it was too late to change back. This experience tought me to fight papers through, unless there is something deadly wrong in them, and I have done this without exception since then.

Now it has almost happened again that I lost a paper. It is based on the diploma work of Gabi Jaritz, which is excellent work that certainly deserves publication. Gabi is a relaxed person and was not pushing me hard enough, so it already took ages before I wrote up the paper. We submitted and received two reports where the referees asked for minor modifications. At that time I was occupied with too many other things, and I postponed the revision. A few months later I was still postponing, although I had carried the paper with me to a number of meetings and conferences where I had hoped to find time to work on it, and I slowly started to realize that I was running into something unpleasant.

To make the long story short, more than one year after receiving the reports I finally brushed up the paper and submitted it to the European Physical Journal B, where it had a smooth refereeing and was finally accepted. I must say that it is a big relief for me, and I am happy that I could defeat the demons of my scientific youth. I owe a big excuse to Gabi for my unduly laziness,  and I truly hope she will accept.

02.05.2011 : Welcome to the Nature club
  (PDF)   doi:10.1038/nphys1992

twin atomsTwin-atom beams is the paper with the shortest title I have ever published, but it's the paper that fills me with the highest joy. Yesterday it was published online in Nature Physics. For a long time in my career I never even thought about publishing in the prestigious Nature and Science journals. The first time I realized that they are not restricted area was back in 2000, when I published my first PRL, a beautiful work together with the group of Eli Kapon which received the highest number of citations of all my papers, while at the same time a work of similar quality was published in Nature.

In the following years more and more of my colleagues succeeded in publishing in Nature and Science, and I was not even chasing the train. It was time to change things. My first attempt failed miserably. The second one was much better, with hindsight I must say that the paper would have deserved it, but we failed closely. All good things go three. Together with the atomchip group of Jörg Schmiedmayer we submitted a beautiful piece of work, which already made it into my news section on 10.12.2010, and I was confident from the beginning that things would work out, as they indeed did in the end.

I am too old to believe that many other occasions will come for reaching science's heaven, and my experience tells me to take a breath and enjoy the moment. My deep thanks go to Julian, Robert, Thorsten and Jörg, as well as to all other coworkers. It was great pushing for this final success.

Presseaussendung KFU Graz    Presseaussendung TU Wien

26.04.2011 : MNPBEM Toolbox

MNPBEM is a Matlab toolbox for the simulation of metallic nanoparticles (MNP), using a boundary element method approach (BEM), which we have developed and used over the last few years. A first release of the MNPBEM toolbox is now ready, which can be made available on the basis of scientific collaborations. The toolbox includes exhaustive demo and help features. It is still in the testing phase and subject to frequent changes, so we advice all users to check the main product page on a regular basis.

29.03.2011 : Best of 2010
  (PDF)   IOP

Today we received the information that our paper Atom interferometry with trapped Bose-Einstein condensates has been selected as one of the Best of 2010 of the New Journal of Physics. According to the journal, this special collection of papers "represents the breadth and excellence of the work published in the journal last year. The articles were selected for their presentation of outstanding new research, receipt of the highest praise from our international referees and the highest number of downloads last year."  There remains nothing for me to amplify this appraisal. I am happy to be part of this exclusive collection of articles, and I thank all co-authors, in particular Jörg for his numerous ideas and suggestions as well as Julian for his tremendous efforts and for compiling everything.

28.03.2011 : Books

As there are no striking news at the moment (but hopefully approaching), I take the opportunity to recommend two books I stepped over recently and which are worth reading. The first one is by my uncle Gottfried Schatz, one of the key persons in the discovery of the mitochondrial DNA. In Feuersucher (NZZ Buchverlag, Zürich, 2011) he describes both the life of a young scientist coming from post-war Austria as well as the race for the discovery of the working principle of ATP synthesis in living cells, that resulted in two nobel prizes (1978 and 1997). The other book, which is real fun to read, is the classical Double Helix by James D. Watson where he gives an autobiographical and very personal account of the discovery of the DNA double helix structure (nobel prize in 1962). Both books imposingly demonstrate how easy science can be if one has the right ideas -- and how tedious otherwise.

29.01.2011 : The rough side of surface plasmons  (PDF)

The influence of surface roughness on the optical properties of particle plasmons is the topic of both a paper that was just accepted by Phys. Rev. B as a rapid communication, and of a research project funded by the FWF that started a while ago. Andi Trügler and Jean-Claude Tinguely from the nanooptics group are working on this project. At the end of 2009 Andi performed the first simulations by adding through a stochastic procedure, that we adapted from simulations for interface roughness in semiconductor quantum wells, surface height fluctuations to a nanosphere. The results were astonishing: virtually nothing happened in the spectra! We tried the same thing with nanorods and the results were extremly similar, although shifts of the plasmon peaks were now at least visible.

It was time to start experiments. Things are more complicated in the experiments because surface roughness is related to the grainy composition of the gold nanoparticles, which not only adds roughness but can also have an impact on the shape of the particles. Nevertheless, we observed again only small deviations between spectra of particles that were identically designed but differ due to the unavoidable surface roughness.

On top of simulation and experiment, we finally added a theoretical description, based on a perturbation theory for surface plasmons, which completed our analysis. The refereeing process was rather rough than smooth, but what else could one expect for a topic like this? I think that we finally delivered a nice piece of work, with many possible extensions, and I am grateful to all collaborators.

18.01.2011 : A new quasiparticle in carbon nanotubes  (PDF)  Phys. Rev.

A few weeks ago we have been asked by PRL to highlight an article reporting the first observation of trions in carbon nanotubes. I consider myself an expert on excitons in semiconductors and a semi- expert on carbon nanotubes, so writing the highlight was OK for me and my co-author Guido Goldoni from Modena university. We tried our best to describe things as clearly as possible and finally delivered something hopefully accessible to a broad community. You may read and judge yourself ...

10.12.2010 : From computer simulations to the lab  (PDF)

About five years ago we started to perform optimal quantum control simulations of Bose-Einstein condensates in magnetic microtraps. The main idea of optimal control is to bring a quantum-mechanical wavefunction from some initial state to a desired target state at a later time. This is achieved by modifying the shape of an external confinement potential, which can be controlled by some external parameters, in an "optimal" way.

Bose-Einstein condensates in atom chips provide an ideal laboratory for such quantum control. On the one hand, condensates are extremely clean quantum systems. On the other hand, variations of the currents running through the wires of the chip provide a highly versatile means for controlling the external magnetic confinement potential. We were extremely lucky to establish a fruitful collaboration with Jörg Schmiedmayer of the atomchip group (TU Vienna), who since the beginning has supplied us with myriads of suggestions and ideas.

In the last few months, Julian Grond has been working hard in the atomchip group and has brought our quantum control simulations to the lab. He has done a great job by devising a protocol for how to optimally modify the external potential in order to shake up the condensate from the ground to the first excited state. The probably more difficult part has been to convince the experimentalists of trying out something that was designed purely through computer simulations, and I owe him a lot of respect for pushing this to the end. At last, the protocol worked out perfectly.

The final paper shows significantly more. It demonstrates that the excited condensate decays into pairs of correlated atoms, similar to the generation of entangled photons in nonlinear optics. I am happy that we could contribute a small piece of the puzzle to this great work and thank the atomchip group for this pleasant collaboration.

10.10.2010 : Junior marathon

zoelauf10 After my sportive summer vacations I have not done too much recently and am currently rather out of shape. My only achievement has been some training runs with my daughter Zoe, who participated this weekend in the Junior marathon of Graz. Zoe was pushing her limits and finished the 3.2 km in 16:25, finally ranking 40th among the 200 starters in the W-U12. Congratulations! If she continues like that, I will have a hard time as a trainer in the future ...

24.09.2010 : Going nano


From Sep. 19 - 23 I attended the 1st Intenational Adriatic School on Nanoscience ASON-1 in Dubrovnik, where I had to give an introduction into the field of nanoscience. I always wanted to attend a (single) talk that would explain what the whole field is about, but it gave me a hard time to prepare something useful for this introduction. At the end I compiled a physics view of nanoscience with some side remarks on biomachines (PDF, 5 MB). In preparing this lecture I read the book "Machinery of life" by David Goodsell and was totally excited by the working principle of biomachines operating in our cells. It is great to see that physics is now approaching bioscience, and I am looking forward to learning more about this exciting field in the next years.

29.07.2010 : Dr. Julian Grond

This friday Julian Grond defended his PhD thesis on Optimal quantum control of trapped Bose-Einstein condensates. The thesis was co-supervised by Jörg Schmiedmayer, and within a monster-exam of two hours we tried to give Julian a hard time. Needless to say that Julian was brilliant and answered our questions properly, although not always in the simplest way. He finally passed with distinction.

Seldomly in my career I have seen someone with such a great passion for physics. Julian is a hard and careful worker and thinker. He approaches problems in the way of a theoretical physicist, but he is able to communicate his results in intuitive terms to a much broader community. With a few exceptions, including writing and presentation, I have learned more from Julian than he has learned from me, and I am grateful for the fruitful time in Graz.

For the next few months Julian will work at the WPI in Vienna, pushing the cooperation with experiment as far as possible, and will then move as a Postdoc to the Cederbaum group in Heidelberg. I wish Julian all the best for the future and hope that he will pursue a career in science and academia. With his skills he certainly deserves this.

25.07.2010 : Bike tour 2010


From July 12th till 22nd, I and my son Moritz, now 15 years old, cycled through the Swiss and Austrian alps. We were lucky with the weather which was very hot, with temperatures typically above 30° C, but we only had a single rain day. Highlights of our tour were the fabulous Grimsel-Furka-Susten round trip (125 km, 3350 hm) and the beautiful Großglockner-Alpenstrasse (75 km, 2100 hm). Moritz was much stronger than last year and crushed the Glockner in 1:15. My progress was more moderate (I was about 30 minutes slower), but we nevertheless both fully  enjoyed our trip. A more detailed tour description (in german) can be found here.

24.06.2010 : Meetings

The end of the summer term is approaching, and as always it is packed with scientific and academic meetings. To make things clear, I have nothing against meetings, most of them are necessary and there has to exist a clear platform for taking decisions. At least I will assume this as a working hypothesis. Nonetheless most meetings fill me with a feeling between depression and aggression: I attend the meeting and wish that I could do something different instead. But hope is alive that the semester will finally come to an end. And then there will be time again for science and other things ...

18.06.2010 : No news but the Kleeblattlauf 2010

There have been complaints that there hasn't been too much new in my news section recently. Unfortunately this is true. The reason is that within the last few months I have been busy writing our program MNPBEM for the simulation of metallic nanoparticles from scratch. The next version will include different materials, layers, and symmetry.

To be honest, I totally underestimated the amount of work needed to write and test such an amount of computer code. I also had to realize that my scientific experience did not help too much in avoiding (stupid) mistakes and spotting them. On June 18, about one hour before our yearly relay race Kleeblattlauf a few minutes of spare time were left, and I was lucky to find an (as usual stupid) mistake that had bothered me for quite a while.

With this relief the run was an easy task. The conditions were perfect, warm and not too humid, and the dark clouds gave us the final motivation to be faster than we would have been otherwise. Our team, Christian Ertler, Walter Pötz, me, and Peter Senekowitsch finished the 4 x 2600 m in 53 minutes, just before the heavy rain set in. Congratulations to the team for this performance.

19.04.2010 : 1 x Mag.

On monday Jürgen Waxenegger passed his final diploma exam with dinstinction. The topic of his thesis was on exciton mapping in carbon nanotubes using plasmonic nanoparticles. Such experiments have been performed in the group of Lukas Novotny, and we tried to find out how far the resolution could be pushed. Maybe even to the mapping of the exciton wavefunction?

Jürgen did a marvellous job and showed that such mapping is indeed possible. I must say that in the last year I was burdened with too many other things, and I did not have as much time for supervision as I wanted. Nevertheless, Jürgen was patient and persistent enough to get the information he needed. Finally, when the thesis was already finished and submitted he was still pushing in order to better understand the results, which finally paid off.

Now its party time for him, which he will hopefully survive ;-) If this is accomplished, I wish him all the best for the future ...

19.04.2010 : Up

I just received an e-mail from Andi Trügler who currently attends a conference in Ascona, monte Veritá. The last two weeks he spent in the Swiss Alps, climbing 8 mountains above 4000 m. Wow !!! I wish I could do the same.

24.03.2010 : PRL paper on LDOS mapping of plasmonic nanoparticles
  (PDF)  Phys. Rev.


This work is Daniel Koller's masterpiece. During his PhD thesis in the nanooptics group he succeeded to fabricate in a two-step lithography process arrays of virtually idenctical metallic nanoparticles together with polymer nanoparticles doped with fluorescing molecules. By varying the relative position between these two types of nanoparticles he could directly map out the photonic local density of states (LDOS), which is of paramount importance for sensor and biosensor applications. The neat thing is that the observation can be done with a normal microscope and does not require any sophisticated measurement device.

I remember that I was totally excited when I first saw the experimental results about a year ago. However, when inspecting the images based on the raw data more closely most features of the plasmonic modes blurred and sharpened again, and it took me a while to convince myself that there was indeed something there. Post processing and coloring of the images (see above) certainly helped a lot.

Our simulation part, which I did together with Andi Trügler, turned out to be quite successful. Once the ingredients were chosen properly, even the quite subtle details of the experiments could be reproduced by our simulations. I think that we finally delivered a fine piece of work. In contrast to other papers of mine and others, which made it into PRL with some luck, this paper certainly deserves publication in this high-impact journal. Congratulations and thanks to all collaborators !!!

18.03.2010 : Publication #100  (PDF)   Phys. Rev.

Finally I crossed the border line of publication #100. The anniversary paper is on cavity-QED with semiconductor quantum dots. Since I am the sole author of the paper it will be a introspective celebration, but that is what it would be anyhow.

At the beginning of my career I hoped that publishing papers would become easier with the years. The contrary proved to be true. In fact, since the beginning almost every paper has been a huge amount of work and a serious struggle. But hopefully this is what keeps us alive.

28.02.2010 : Ski race Mauterndorf 

The Winterschool Mauterndorf 2010 on "New Developments in Solid State Physics" was great, as usual. Our mission for the final ski race was to defeat the "Flachländer" (flat-landers), and Gabi and I joined the team of Friedemar Kuchar (Leoben) and Klaus Lischka (Paderborn). We failed miserably. The Berlin (!) team NANO FLASH of Dieter Bimberg won, and our team only came in fourth ...    (full list of results, photo of Artur Zrenner)

17.01.2010 : Skiing (the hard way)

winter 2010winter 2010

Welcome to winter 2010! Contrary to what the left picture suggests, the snow conditions are still rather poor. Nevertheless, we are having fun with skiing, sometimes exploring the beauty of botany (picture on rhs).  pictures taken by Robert Breininger

23.12.2009 : End of the year

It has been a long and busy year. Up to the last moment we have been working on two long papers which we hoped to finish in 2009. However, now it's time to give in and let things go. Next year there will be plenty of time to finish old projects and to start new ones. I wish everybody a good festive break!

29.10.2009 : Solid state goes for chocolate

As a sweet goodbye for Eta and Gabi the solid-state group organized a visit to the Zotter chocolate factory in Riegersburg, with chocolate tasting until we had enough ...

Pictures by Peter Senekowitsch

14.10.2009 : 2 x Mag.a

Within a week both of my female diploma students, Gabi Jaritz and Hajreta Softic, graduated. It has been a great pleasure to have had them in my group!

Gabi started quite a while ago, and the topic of her thesis was on quantum-dot based single and entangled photon sources. She had a hard time because the topic was not overly well defined (my fault!) , but she did a great job and finally submitted a really impressive thesis. Gabi is more on the quiet side, and it thus took me a while to figure out how strong she is in physics! She now took a timeout to decide where to go in the future.

Eta did her thesis on the lifetime changes of quantum emitters close to metallic films, a topic that was motivated by our collaboration with the KFU nanooptics group. To compute the dyadic Green tensor we followed the book of Chew, which turned out to be a hard endeavour when it came to the technicalities. Eta was pushing hard to understand things thoroughly and to complete her work fast. Maybe things would have been easier with a slightly more relaxed attitude, but this seems to be in contrast to Eta's strong personality. Nevertheless, she finally submitted a fine piece of work and passed her final exam with distinction.

I (and my group) will certainly miss both of you. And whatever you will do in the future: good luck and all the best !!!

12.10.2009 : Solid runners

On october 11, 2009, the "solid-state runners" Peter Senekowitsch, Gabi Jaritz, and Julian Grond finished together with the "high-energy runner" Faruk Geles the Graz Marathon 2009 in 3:58:09. Congratulations, and keep on running!

05.10.2009 : PRA paper on atom chips
   (PDF)   Phys. Rev. 

This paper has been around for quite a while. It is based on one of Jörg Schmiedmayer's (numerous!) suggestions to use optimal control theory in order to maximize the performance of atom-chip interferometers by reducing atom number fluctuations. Julian started to work on this problem more than two years ago, and obtained his first results for a simplified two-mode model soon.

What came next was a tedious research struggle, where we tried to figure out whether our conclusions would also prevail under realistic conditions. Julian did a marvelous job and carefully analyzed every detail. In the process of understanding things more deeply it became necessary to rewrite the paper several times, and for a while it seemed as if the paper would never come to an end. I am glad that Julian was patient enough and finally completed his masterpiece, which had the smoothest refereeing process I have ever seen. Congratulations!

28.08.2009 :
PRL paper on EELS of plasmonic nanoparticles  (PDF)  Phys. Rev.

About a year ago we started to think about the question what kind of information Electron Energy Loss Spectroscopy (EELS) provides about plasmonic nanoparticles: is it the field enhancement? or the LDOS? or something else?  

Our work was motivated by a paper of Garcia de Abajo et al. that suggested that EELS can directly probe the LDOS. Together with Hari Ditlbacher and Jo Krenn from the nanooptics group, who are planning to utilize EELS to extract optical information of plasmonic nanoparticles, we started to run simulations for the particle shapes we are interested in. Altough we were expecting a reasonable answer to our question, it soon turned out that EELS is not closely related to any of the optical quantities.

At some point we decided to write up our conclusions and submitted the paper. It was the beginning of a longish story. The paper was sent to a friendly but picky referee, who was not fully convinced by our conclusions and asked several questions, which forced us to think more deeply about the relation between EELS and LDOS. In the following, the manuscript went through several iterations until it converged to a form acceptable for us and the referee. The quality of the paper has certainly considerably improved during this process, and I feel that this is a very nice example of how critical but constructive referees can play an invaluable role in the refereeing process. So, whoever pushed us into the right direction: thanks a lot!

28.08.2009 : With the bicycle from Austria to Paris


From 09.08.2009 to 25.08.2009 me and my son Moritz, 14 years, went with the bikes from Grundlsee (Austria) to Paris. We had fixed the tour about a year ago and it horrified me for quite a while. However, things turned out perfectly and we were extremely lucky with the weather. After 11 days of work and one rest day we arrived in Paris, where we stayed for additional 5 days togehther with the rest of the family. With hindsight, it was a fun tour and less exhausting than expected, but probably I already forgot all the pain and desperation. It's great to have kids who are still pushing us to our (physical) limits!


After running this website for about two years, I realized that certain news, regarding the group members or research, did not fit into the existing structure. In the future, the novel News section is thus intended to provide some background information about recent research highlights or achievements of the group members on a hopefully (!) regularly basis.

Ulrich Hohenester
Institut für Physik, Karl-Franzens Universität Graz, Austria