News (2009 - 2010).
12.12.2014 : MNPBEM toolbox -- substrates and layer structures
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
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
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
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
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
On 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
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
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
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
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
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
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
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)
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
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
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:
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
10.04.2014 : The edge of glory
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)
The 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
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
A 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
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
Finally, 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
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 (PDF)
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
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)
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
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
30.07.2013 : Tomography of plasmon fields (PDF)
30.07.2013 : Late greetings from Jyväskylä
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
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
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
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
Last 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
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
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
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
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.
12.11.2012 : The future of plasmonics (and different things)
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
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
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
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
Finally 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
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
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
with one or two beers. Congratulations and thanks to
22.06.2012 : Teaching electrodynamics
24.03.2012 : Twin atoms reloaded
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
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
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
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.
19.03.2012 : Hungarian evergreen
Last 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
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!
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
". So thanks a lot to Gabor, Zsolt, as well as to the unknown referee!
22.02.2012 : 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
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
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
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
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
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
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
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
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
23.08 - 01.09.2011 : Bike tour through the dolomites
01.08.2011 : Prime numbers
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.
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
17.06.2011 : Kleeblattlauf 2011
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.
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
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
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
02.05.2011 : Welcome to the Nature club
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
, 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
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
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
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
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
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
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
24.09.2010 : Going nano
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 ...
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
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
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
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
24.03.2010 : PRL paper on LDOS mapping of plasmonic nanoparticles
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
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
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)
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
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
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
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
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
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
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.
28.08.2009 : With the bicycle from Austria to Paris
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!
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!
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.