Münchner Physik-Kolloquium / Munich Physics Colloquium

2015
PhysikKolloquium
Sommer
Münchner
Vortragsprogramm mit Abstracts
Beginn der Veranstaltungen ist um 17:15 Uhr. München.
Sämtliche Vorträge sind öffentlich bei freiem Einbezeichnet Vorträge im Hörsaal 2 des Physiktritt. Die Art der Nachsitzung wird in der VeranstalDepartments
/ TUM am Forschungsgelände in
tung bekannt gegeben.
Garching. Das Forschungsgelände kann mit der U6
bezeichnet Vorträge im Hörsaal H 030 der (bis Garching-Forschungszentrum) erreicht werFakultät für Physik / LMU in der Schellingstraÿe 4, den.
Quantum Einstein equations in loop
quantum gravity
Prof. Dr. Kristina Giesel
2015-04-20
Department für Physik, Friedrich-Alexander-Universität,
Erlangen-Nürnberg
Loop quantum gravity is a candidate for a theory
of quantum gravity, which takes general relativity
as its classical starting point. The quantum theory is obtained by applying canonical quantization
to general relativity. For this purpose, the techniques known from quantum eld theory need to
be generalized. As a consequence, loop quantum
gravity is based on a quantum eld theory, which
is in many aspects different from the quantum
eld theory, that is used to formulate the Standard Model of particle physics. The dynamics of
the quantum theory is described by the so called
quantum Einstein equations, the quantum analog
of Einstein's equations. After a brief introduction to
the ideas and concepts of loop quantum gravity,
we will discuss the current status of the dynamics,
particularly the role of gauge invariance in this context and also present further research directions
currently addressed in loop quantum gravity.
ranging from protein synthesis, ATP synthesis,
molecular binding and recognition, selective transport, sensor functions, mechanical stability, and
many more. The combined interdisciplinary efforts
of the past years have revealed how many of these functions are effected on the molecular level.
Computer simulations of the atomistic dynamics
play a pivotal role in this enterprise, as they offer
both unparalleled temporal and spatial resolution.
With state of the art examples, this talk will illustrate the type of questions that can (and cannot)
be addressed, and its (current) limitations. The examples include aquaporin selectivity, mechanics of
energy conversion in F-ATP synthase, and tRNA
translocation within the ribosome. We will further
demonstrate how atomistic simulations enable one
to mimic, one-to-one, single molecule experiments
such as FRET distance measurements, and thereby to enhance their accuracy. We will, nally, take
a more global view on the `universe' of protein
dynamics motion patterns and demonstrate that a
systematic coverage of this `dynasome' allows to
predict protein function more reliably than purely
structure-based methods.
Forces and conformational dyna- Is solid helium a quantum crystal?
mics in biomolecular nanomachines Prof. Dr. Sebastien Balibar
Prof. Dr. Helmut Grubmüller
2015-05-04
2015-04-27 Department of Physics, Ecole Normale Superieure and
Max-Planck-Institut für biophysikalische Chemie,
Theoretical and Computational Biophysics, Göttingen
CNRS, Paris, France
It had been proposed that super uidity could coProteins are biological nanomachines. Virtually exist with crystalline order in solid helium, thanks
every function in the cell is carried out by proteins its quantum properties. If true, solid helium would
The understanding of glasses remains one of the
grand challenges in condensed matter: glasses
have liquid-like structure, but exhibit solid-like properties. These materials inspire us to rethink the
notion of ow and rigidity of solids. Indeed, recent theoretical concepts suggest that material
ow can be understood universally as new critical
phenomenon, connecting the atomic-scale ow of
glasses to the motion of tectonic plates in earth
quakes. Experimentally, new ``soft glasses'' such
as colloidal suspensions, foams and emulsions,
have evolved as important model systems to directly visualize the particle-scale ow of solids: the
individual constituent particles with sizes between
a micrometer and a millimeter can be imaged and
tracked accurately in three dimensions and real
time, allowing direct experimental insight into the
physics of ow of glasses. In this talk, I will review
the progress in this rapidly developing eld. Based
on real-space observations in colloidal glasses,
I will demonstrate the hierarchical organization of
ow in glasses, and provide evidence for new kinds
of phase transitions that indeed seem to underlie
the transition from rigid to owing matter. In addition to the direct imaging of the constituent particles
and their dynamics, hard-sphere systems have the
advantage that the particle con gurations provide
a direct route to the free energy of the system. I
will exploit this relation to elucidate the interplay
of strain build-up and relaxation, and according
(structural) free energy changes during the ow
and aging of glasses.
have been be the rst `supersolid'. For some years,
one thought that this paradoxical coexistence of
order in real and momentum space named `supersolidity' had been observed by several groups
in the world. But nowadays, we understand that
supersolidity does not exist in these crystals, but
instead the mobility of their dislocations is so high
in the low temperature limit and if all impurities are
suppressed, that it does not resist to shear in some
directions. The discovery of this `giant plasticity' in
helium crystals is not less interesting than supersolidity. Its careful analysis has led to fundamental
progress in the knowledge of dislocation networks
and dynamics, which are basic phenomena at the
origin of the plasticity of materials. Now a question
remains: in the end, what is really quantum in these
crystals? I will try to give some answers to it.
Energy and signal
cules
Prof. Dr. Gerhard Stock
ow in biomole2015-05-11
Biomolecular Dynamics, Institut für Physik, AlbertLudwigs Universität, Freiburg
In biomolecules, the transport of heat and vibrational energy occurs within (tens of) picoseconds.
The propagation of conformational change in intramolecular signaling, on the other hand, is believed
to occur on a much longer time scale of say,
nano- to milliseconds. Interestingly, recent experiments and simulations indicate a possible connection between these fast and slow processes, e.g.,
via the notion that allosteric interactions may be
of dynamical nature. To investigate these intriguing phenomena, transient infrared experiments
on photoswitchable peptides and proteins are a
powerful approach. Accompanying theses experimental studies, nonequilibrium molecular dynamics simulations allow us to study the mechanisms of energy transport and the transport of
conformational change. We show that the energy
ow in biomolecules is indeed fast and anisotropic, and can affect resides quite distant from the
heat source. Transport of conformational change
in a photoswitchable PDZ2 domain, on the other
hand, is found to occur in various stages from
pico- to microseconds, which may re ect elastic
deformation, (de-)stabilized interactions and conformational transitions.
Molecular systems engineering with
DNA
Prof. Dr. Hendrik Dietz
2015-06-01
Biomolekulare Nanotechnologie, Zentrum für Nanotechnologie und Nanomaterialien, Technische
Universität München
It is notoriously dif cult to observe, let alone control, the position and orientation of molecules because of their small size and the constant thermal uctuations that they experience in solution.
Molecular self-assembly with DNA provides a route for placing molecules and constraining their
uctuations in user-de ned ways and with up to
Flow of glasses: new insight into an Angstroem-scale
precision. These positioning opold mystery
tions open attractive and unprecedented avenues
Prof. Dr. Peter Schall
2015-05-18 for scienti c and technological exploration. In my
Institute of Physics, University of Amsterdam, The talk I will introduce some of the key concepts
and methods, and highlight a number of recent
Netherlands
developments.
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The physics of information: from
Maxwell's demon to Landauer
Prof. Dr. Eric Lutz
is reproducible only because of error correction
mechanisms? Or might each step be more reliable than previously intuited, squeezing as much
information as possible out of a limited number of
molecules? Using the fruit y as a model system,
our recent work shows that from the macroscopic
features of the body plan precision can be traced, through several steps, back to the counting
of essential signaling molecules placed in the egg
by the mother. Absolute concentrations of molecules are reproducible to better than 10%, which
translates to a spatial accuracy in a developing
embryo suf cient to distinguish each cell from its
neighbor, arguably the highest precision that the
organism could achieve. These results argue for
an evolutionary design principle by which developmental systems operate near an optimal level
of precision.
2015-06-08
Department für Physik, Friedrich-Alexander-Universität,
Erlangen-Nürnberg
We will discuss the intimate connection existing
between information theory and thermodynamics
following its historical development. We will focus
on two complementary aspects: 1) the gain of information which we will illustrate with Maxwell's
famous demon and 2) the erasure of information summarized by Landauer's principle. We will
further present a number of recent single-particle
experiments that have for the rst time realized the
above gedanken experiments in the lab.
Synthetic neural systems
Prof. Dr. Karlheinz Meier
2015-06-15 Arti cial graphene in nanopatterned
GaAs quantum wells
Kirchhoff-Institut für Physik, Universität Heidelberg
Prof. Dr. Aron Pinczuk
Viewed with the eyes of a physicist some aspects
the brain can be described by a classical multiparticle approach. Major differences between living and physical matter arise from the facts that
constituents of the brain are active information processing units and that their interactions are changing with time. Also, the brain is not an isolated
system but develops as a result of interaction with
the environment. These facts limit the applicability of analytical methods and even simulations on
traditional high performance computers are hindered by energy and timing constraints. The lecture
will introduce the idea of implementing synthetic neural circuits as physical models which offer
several orders of magnitude advantages over the
simulation approach in terms of energy and time.
2015-06-29
Department of Applied Physics and Applied Mathematics and Department of Physics, Columbia University,
NY, USA
The honeycomb topology, natural graphene is a
benchmark, supports states for electrons that disperse as mass less Dirac fermions. A novel and
powerful way to achieve Dirac fermions in a controlled manner is to create arti cial graphene (AG)
in the form of a honeycomb lattice potential superimposed on a semiconductor quantum well (QW).
This talk reports on the realization and characterization of very short period AG topology for 2D
electron systems in GaAs QWs. Short AG periods reaching as low as 40 nm enable formation
of well-de ned Dirac fermions around K and K'
points of the AG Brillouin zone. Evidence of formation of well-de ned Dirac fermion states is found
in spectra of excitations built from transitions of
electrons between bands of the AG potential measured by resonant inelastic light scattering (RILS).
The honeycomb lattice potential is imprinted on
a modulation-doped GaAs QW sample by means
of state-of-the-art e-beam lithography followed by
low-disorder inductively coupled plasma reactiveionetching. The results of our research show that
arti cial potentials in semiconductors provide fruitful platforms for exploration of novel physics with
potential applications.
Bridging scales in development:
from single molecules to macroscopic biological patterns
Prof. Dr. Thomas Gregor
2015-06-22
Joe-Henry Laboratories of Physics and Lewis-Sigler
Institute for Integrative Genomics, Princeton University,
Princeton, NJ, USA
Identical body plans across a species result from
precise and reproducible embryonic development.
However, the environment for developmental processes can be quite variable, and crucial signals
inside the embryo are carried by so few molecules Double disk dark matter
that we might expect development to be noisy. It
2015-07-06
is thus unclear how precision is achieved along the Prof. Dr. Lisa Randall
developmental path. Should we imagine that every Department of Physics, Harvard University, USA
step in the process is sloppy, so that the result I'll review dark matter proposals and describe more
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separated by a tunable micrometer sized gap.
We observe the strong exciton-photon coupling
regime and formation of exciton-polariton eigenstates, whose energy can be tuned by changing
the gap between the DBR mirrors. Furthermore,
we demonstrate that the magnitude of the characteristic anti-crossing between the cavity modes
and the MoSe2 excitons (a Rabi splitting) can be
enhanced by embedding a multiple-QW structure,
containing two MoSe2 monolayers separated by
an hBN barrier. At a temperature of 4 K, for a
single QW sample the vacuum Rabi splitting of
20 meV is observed for the neutral exciton state,
which is increased to 29 meV for the double QW,
following closely the NQW dependence. An intermediate coupling regime is observed for the
charged exciton, where the polariton states are
not fully resolved as the Rabi splitting is similar to
the charged exciton linewidth. This work opens a
new avenue in the eld of polaritonics in a new
material system of van der Waals crystals and heterostructures with a potential for polariton devices
operating at room temperature.
recent work.
Exciton-polaritons in van der Waals
heterostructures embedded in tunable microcavities
Prof. Dr. Alexander Tartakovskii
2015-07-13
Department of Physics and Astronomy, University of
Shef eld, UK
Monolayer lms of van der Waals crystals of transition metal dichalcogenides (TMDCs) are direct
band gap semiconductors exhibiting excitons with
very large binding energies and small Bohr radii,
leading to a high oscillator strength of the exciton
optical transition. Here we report fabrication of `van
der Waals quantum wells' (QW) made from molybdenum diselenide (MoSe2 ) light-emitting monolayers and hexagonal boron nitride (hBN) barriers.
Such heterostructures are embedded in an optical
microcavity consisting of a concave and a planar dielectric distributed Bragg re ectors (DBR)
Allgemeine Informationen
Das Münchner Physik-Kolloquium ist das Podium der physikalischen Forschung im Münchner Raum. Es wird gemeinsam von den beiden
Universitäten und den entsprechenden MaxPlanck-Instituten veranstaltet. Die Vorträge berichten über aktuelle Themen der Physik und
angrenzender Gebiete und spiegeln den interdisziplinären Charakter der modernen Physik
wider.
Es ist erklärtes Anliegen des Münchner PhysikKolloquiums, die räumliche Trennung der Physik
in die verschiedenen Forschungsstandorte in München und Garching durch eine gemeinsame Veranstaltung zu überbrücken. Dazu soll auch der
alternierende Wechsel des Veranstaltungsorts beitragen.
Veranstaltende Einrichtungen
Max-Planck-Institut für Physik
Die Darstellung wird möglichst allgemeinverständ- Föhringer Ring 6, 80805 München
lich gehalten, um auch physikalisch interessierte MPI-Koordinator: Dr. F. Simon
Zuhörer aus dem industriellen oder schulischen Technische Universität München
Bereich anzusprechen. Die Vortragenden sind aus- Physik-Department, James-Franck-Straÿe 1,
gewiesene Fachleute auf dem jeweiligen Gebiet, 85748 Garching
zum Teil auch neu nach München berufene Wis- TUM-Koordinatoren:
senschaftler, die sich in diesem Rahmen einer Prof. M. Zacharias, Prof. J. Finley
breiteren Öffentlichkeit vorstellen wollen. Das Kolloquium stellt insbesondere für die Studenten der Ludwig-Maximilians-Universität München
Physik eine einfache Möglichkeit dar, im Laufe Fakultät für Physik, Schellingstraÿe 4,
eines Jahres alle wichtigen Arbeitsgebiete der ge- 80799 München
genwärtigen physikalischen Forschung kennen zu LMU-Koordinatoren:
Prof. L. Pollet, Prof. J. Weller
lernen.
Aktuelles Programm: http://www.ph.tum.de/kolloquium
nanosystems initiative munich
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