Plenarvorträge - DPG-Tagungen

Dynamik und Statistische Physik Donnerstag
as a prototype. We calculate the scattering probability matrix elements
| Sn,m | 2 , wave functions, and Husimi distributions for a set of geometrical
parameters producing weak, mixed, and strong chaotic ray dynamics.
Comparison of these quantities with their classical counterparts allows
us, on the one hand, to understand important global properties of waveguides
in terms of purely classical dynamics and, on the other, to unveil
drastic differences between wave and particle behavior. Further, we compare
our predictions with experimental results obtained in a microwave
realization of the cosine billiard.
DY 46.42 Do 16:00 Poster D
How optical microresonators radiate — •Martina Hentschel 1
and Henning Schomerus 2 — 1 Department of Physics, Duke University,
Durham, NC 27708-0305, U.S.A. — 2 MPI Physik komplexer Systeme,
Noethnitzer Str. 38, D-01187 Dresden
Optical microresonators have broad application potential in optical
communication devices, and are interesting model systems in the field
of Wave Chaos. Most of our qualitative understanding of their radiation
characteristics rests on the simple ray-optics picture, which however
requires a wave length much smaller than the geometric features of
the system. This is not realized in the most interesting applications. We
highlight effects that lead to substantial deviations from the ray picture.
Notably, at curved interfaces, the Goos-Haenchen effect causes deviations
from both Snell’s and Fresnel’s laws. We analyse the resulting deviations
in the radiation characteristics using four appropriately defined Husimi
functions, corresponding to incident and emerging rays on either side of
the interface. These four phase-space representations of the electromagnetic
wave function naturally allow to read-off the radiation directions,
and replace the single Husimi function used in hard-wall systems.
DY 46.43 Do 16:00 Poster D
Stochastic Webs and Localization in a Quantum Mechanical
Kick System — •Ulf Martin Engel and Peter Eckelt — Institut
für Theoretische Physik, Universität Münster, Wilhelm-Klemm-Straße 9,
D-48149 Münster
The classical kicked harmonic oscillator is characterized by a very special
scenario of weak chaos: in the case of resonance between the eigenfrequency
of the harmonic oscillator and the frequency of the periodic
forcing, periodic stochastic webs in phase space are generated [1]. We
investigate the quantum dynamics [2] of this model system and show
that the resulting Husimi distributions in quantum phase space exhibit
the same web-like structures as in the classical case. The quantum dynamics
is characterized by diffusive energy growth — just as the classical
dynamics in the channels of the webs. In the case of nonresonance, the
classically diffusive dynamics is quantum mechanically suppressed. We
explain this bounded energy growth (which corresponds to localization
in quantum phase space) by mapping the system onto the Anderson
model, in a way that is motivated by the standard treatment of the quantum
kicked rotor [3].
[1] G. M. Zaslavsky et al., Weak Chaos and Quasi-Regular Patterns,
Cambridge University Press, Cambridge 1991. [2] G. P. Berman,
V. Y. Rubaev and G. M. Zaslavsky, Nonlinearity, 4 543 (1991).
[3] S. Fishman, D. R. Grempel and R. E. Prange, Phys. Rev. Lett. 49,
509 (1982). [4] U. M. Engel, Dissertation Universität Münster (2003).
DY 46.44 Do 16:00 Poster D
Path integral approach to the dissipative curve-crossing dynamics
— •Alexey Novikov 1,2 , Ulrich Kleinekathöfer 1,2 , and
Michael Schreiber 2 — 1 International University Bremen, Bremen,
Germany — 2 Institut für Physik, Technische Universität Chemnitz,
Chemnitz, Germany
The dynamics of a curve-crossing system is considered using path integrals
in a combined phase space and coherent state representation.
The relevant system consists of two one-dimensional potential energy
surfaces, the dissipation is described by its interaction with the bath
of non-interacting harmonic oscillators. The Lagrangian function of the
electronic subsystem is written in the coherent state representation using
mapping approach while the vibrational degrees of freedom are treated
by the Feynman-Vernon path integral. The non-Gaussian part of the
path integral is calculated by introducing the effective bias and hopping
constants for the electronic states. Finally, the dynamics of a Gaussian
wave packet and the population of electronic levels is analyzed within
the presented method.
DY 46.45 Do 16:00 Poster D
Non-Markovian density matrix theories based on the decomposition
of the spectral density — •U. Kleinekathöfer 1,2 and M.
Schreiber 2 — 1 International University Bremen, 28725 Bremen, Germany
— 2 Institut für Physik, Technische Universität Chemnitz, 09107
Chemnitz
For the description of dynamical effects in quantum mechanical systems
on ultra-short time scales memory effects play an important role.
Here we propose two different theories [1] which are either based on
the time-convolution Nakajima-Zwanzig projection operator formalism
or the time-convolutionless Hashitsume approach. The proposed theories
as well as the method by Meier and Tannor [2] are based on a numerical
decomposition of the spectral density. For the example of the damped
harmonic oscillator these non-Markovian theories are compared among
each other, to Markovian approaches neglecting the memory effect and to
path integral calculations. Some of the proposed non-Markovian theories
treat explicitly time-dependent system Hamiltonians nonperturbatively.
Therefore these method can be used for the description of experiments
with arbitrary large laser fields.
[1] U. Kleinekathöfer, J. Chem. Phys. (submitted).
[2] C. Meier and D.J. Tannor, J. Chem. Phys. 111, 3365 (1999).
DY 46.46 Do 16:00 Poster D
PHASE BEHAVIOUR AND ELASTICITY OF COLLOIDAL
MODEL SUSPENSIONS — •Larysa Shapran, Patrik Wette,
Hans Joachim Schöpe, and Thomas Palberg — Johannes
Gutenberg-University Mainz, Institute of Physics, Staudinger Weg 7,
D-55099 Mainz
We have measured the phase behaviour and the elasticity of crystallizing
systems of submicron polystyrene spheres in low salt aqueous suspension.
Microscopy and static light scattering (SLS) yield the fluid-crystal
transition lines including the coexistence region in the particle number
density n salt concentration c plane. SLS shows further that the crystal
phase is b.c.c. Torsional resonance spectroscopy [1] yields the static
shear modulus G, which is observed to increase with n at constant c=0
and to decrease at n=const with increasing c. We compare our phase
behaviour predictions from computer simulation [2,3] using the effective
charge Z*(n,c) derived from the elasticity measurement. Use of the elasticity
effective charge instead of previously often employed conductivity
charge improves the consistency significantly.
[1] H.J.Schöpe, T.Palberg, J. Colloid Interface Sci. 234, 149-161 (2001)
[2] M.O.Robbins, K.Kremer and G.S.Grest, J. Chem. Phys. 88, 3286
(1988)
[3] E.J.Meijer and D.Frenkel, J. Chem. Phys. 94, 2269 (1991)
DY 46.47 Do 16:00 Poster D
Solid friction at model metal interfaces studied via NEMD computer
simulations — •Igor Stankovic 1 , Martin Kröger 2 , and
Siegfried Hess 1 — 1 Institute of Theoretical Physics, PN 7-1, Technical
University of Berlin, Hardenbergstr. 36, D - 10623 Berlin — 2 Polymer
Physics, ETH Zurich, ML H18, Sonneggstr. 3, CH-8092 Zurich
The embedded atom method is adopted to study structural changes
and mechanical alloying at model metal interfaces during dry solid friction
[1,2,3]. The main constitutive properties of real metals, i.e., cohesive
energy, elastic constants, and heat of solution, are reproduced by a set
of a few basic model parameters. The model metal is subjected to shear
deformation and strong flow via non-equilibrium molecular dynamics in
order to discuss the origins of some qualitative properties observed more
specific embedded atom potentials. The mechanisms leading to mechanical
alloying at interface are observed and discussed [3]. Information about
crystal structure inside NEMD configurations is obtained with ”common
neighbor analysis”, based on planar graphs [4].
1. M. S. Daw and M. I. Baskes, Phys. Rev. Lett. 50, 1285 (1983).
Phys. Rev. B 29, 6443 (1984).
2. I. Stankovic, M. Kröger, and S. Hess, Phys. Rev. E, accepted 2003.
3. M. Kröger, I. Stankovic, and S. Hess, Multiscale Model. Simul. 1,
25-39 (2003).
4. I. Stankovic, M. Kröger, and S. Hess, Comput. Phys. Commun. 145,
371 (2002).