Plenarvorträge - DPG-Tagungen
Plenarvorträge - DPG-Tagungen
Plenarvorträge - DPG-Tagungen
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Tiefe Temperaturen Montag<br />
ticity. As a model it is suggested that the turbulent state breaks down<br />
when a fluctuation crosses a threshold level. Applying Rice’s formula for<br />
the average level crossing per unit time of a stationary normal process<br />
gives information on the probability density function and the spectral<br />
bandwidth of the fluctuations. As a result a normal distribution is found<br />
and the standard deviation as well as the spectral bandwidth are determined<br />
quantitatively. In addition to superfluid turbulence this model<br />
may be applicable also to other instabilities which result from random<br />
fluctuations exceeding a certain threshold.<br />
TT 4.3 Mo 10:45 H19<br />
Ground state properties and non-equilibrium dynamics of<br />
hard-core bosons confined on optical lattices — •Marcos<br />
Rigol Madrazo and Alejandro Muramatsu — Institut fuer<br />
Theoretische Physik III, Universitaet Stuttgart, Pfaffenwaldring 57,<br />
D-70550 Stuttgart, Germany<br />
We study by means of an exact numerical approach, a gas of hard core<br />
bosons (HCB) confined on optical lattices. The ground state properties<br />
of such systems are analyzed. Local incompressible phases appear in the<br />
system, like in the case of interacting soft-core bosons [1] and fermions<br />
[2,3]. The changes in momentum distribution function and in the natural<br />
orbitals (effective single particle states) introduced by the formation<br />
of such phases are analyzed. We also study non-equilibrium properties<br />
for those systems, which within our numerical approach can be obtained<br />
exactly for systems with ∼ 200 particles on lattices with ∼ 3000 sites.<br />
In particular we analyze the free expansion of the gas when it is released<br />
from the trap turning off the confining potential. We show that the expansion<br />
is non-trivial (as opposed to the fermionic case) and new features<br />
to be observed in the experiments are analyzed.<br />
[1] G. G. Batrouni, V. Rousseau, R. T. Scalettar, M. Rigol, A. Muramatsu,P.<br />
J. H. Denteneer, and M. Troyer, Phys. Rev. Lett. 89, 117203<br />
(2002).<br />
[2] M. Rigol, A. Muramatsu, G. G. Batrouni, and R. T. Scalettar, Phys.<br />
Rev. Lett. 91, 130403 (2003).<br />
[3] M. Rigol and A. Muramatsu, cond-mat/0309670 (2003).<br />
TT 4.4 Mo 11:00 H19<br />
Ultracold fermions and the SU(N) Hubbard model — •Carsten<br />
Honerkamp 1 and Walter Hofstetter 2 — 1 MPI Solid State Research,<br />
Stuttgart — 2 MIT, Cambridge, USA<br />
We investigate the fermionic SU(N) Hubbard model on the twodimensional<br />
square lattice for weak to moderate interaction strengths<br />
using one-loop renormalization group and mean-field methods. For the<br />
repulsive case U > 0 at half filling and small N the dominant tendency<br />
is towards breaking of the SU(N) symmetry. For N > 6 staggered flux<br />
order takes over as the dominant instability, in agreement with the large-<br />
N limit. Away from half filling for N = 3 the system rearranges the<br />
particle densities such that two flavors remain half filled by cannibalizing<br />
the third flavor. In the attractive case and odd N a full Fermi surface<br />
coexists with a superconductor in the ground state. These results may<br />
be relevant to future experiments with cold fermionic atoms in optical<br />
lattices.<br />
TT 4.5 Mo 11:15 H19<br />
Self-energy and critical temperature of weakly interacting<br />
bosons — •Peter Kopietz, Sascha Ledowski, and Nils Hasselmann<br />
— Institut für Theoretische Physik, Universität Frankfurt,<br />
Robert-Mayer-Str. 8, 60054 Frankfurt/Main<br />
Using the exact renormalization group we calculate the momentumdependent<br />
self-energy Σ(k) at zero frequency of weakly interacting bosons<br />
at the critical temperature Tc of Bose-Einstein condensation in dimensions<br />
3 ≤ D < 4. We obtain the complete crossover function interpolating<br />
between the critical regime k ≪ kc, where Σ(k) ∝ k 2−η , and the<br />
short-wavelength regime k ≫ kc, where Σ(k) ∝ k 2(D−3) in D > 3 and<br />
Σ(k) ∝ ln(k/kc) in D = 3. From our Σ(k) we find for the interaction-<br />
induced shift of Tc in three dimensions ∆Tc/Tc ≈ 1.23 an 1/3 , where a is<br />
the s-wave scattering length and n is the density [1].<br />
[1] S. Ledowski, N. Hasselmann, and P. Kopietz, cond-mat/0311043.<br />
TT 4.6 Mo 11:30 H19<br />
Reflectionless dynamics of 1D charge and spin modes in atomic<br />
traps — •Lars Kecke, Wolfgang Häusler, and Hermann<br />
Grabert — Physikalisches Institut, Albert- Ludwigs Univerität,<br />
Freiburg<br />
Gases of Fermionic atoms in cigar shaped, one-dimensional traps provide<br />
an ideal means to study the dynamics of correlated Fermi systems<br />
in the Tonks gas limit of repulsive contact interactions. The interaction<br />
strength can be tuned experimentally [1].<br />
Based on the Tomonaga-Luttinger (TL) model we present calculations<br />
on the dynamics of charge and spin density waves. Particularly at the<br />
edge both modes show features that are strikingly different from the<br />
non-interacting case as well as from conventional TL dynamics. For example<br />
we find a suppression of reflections that should be experimentally<br />
observable.<br />
[1] T. Loftus et al PRL 88, 173201 (2002)<br />
TT 4.7 Mo 11:45 H19<br />
Audio Demonstration of Quantum Oscillations: Phase Locking<br />
of Josephson Oscillations in superfluid 3He-B — •S.V.<br />
Pereverzev and G. Eska — Physikalisches Institut, Universität<br />
Bayreuth<br />
We report on a family of dynamic effects which were observed in superfluid<br />
3He flow through a weak link (array of 65x65 holes of 150 nm dia.<br />
in a 50 nm SiN membrane). The flow was driven by a time dependent<br />
pressure difference (∆p(t)) to which an ac-modulation (paccos(ωt + θ))<br />
was added. A self-trapping phase-locked state could be observed when the<br />
Josephson frequency (ωJ(t) = ∆p(t)<br />
) and the ac-drive frequency ω merged<br />
ρκ0<br />
(reverse AC-Josephson effect). This trapped state is a zero net current<br />
state with a nonzero pressure difference across the weak link. Close to<br />
this resonance the observed beat frequency ωJ − ω clearly indicates the<br />
presence of Josephson oscillations which can be heared. Low frequency oscillations<br />
around this quasi-equilibrium state were also observed, as well<br />
as Helmholtz oscillations around the zero pressure-difference equilibrium<br />
state. The frequencies of both of these oscillatory modes depended on<br />
amplitude and frequency of the ac-drive. For the pressure driven flow we<br />
measured unexpected high losses. The origin of these losses is unclear.<br />
TT 4.8 Mo 12:00 H19<br />
Resonant Transport of Bose-Einstein Condensates — •Tobias<br />
Paul, Peter Schlagheck, and Klaus Richter — Institut für theoretische<br />
Physik, Universität Regensburg<br />
Due to the rapid progress of “atomic chip” technology [1], the implementation<br />
of experiments probing the propagation of Bose-Einstein<br />
condensates in mesoscopic waveguides becomes feasible. A particular interesting<br />
waveguide geometry is the double barrier structure created by<br />
a sequence of two constrictions, which can serve as a Fabry-Perot-like<br />
interferometer for the condensate [2]. In this context the question arises<br />
how the presence of repulsive interactions between the condensed atoms<br />
influences the transmission through this double barrier structure. Our numerical<br />
approach is based on the Gross–Pitaevskii equation and employs<br />
absorbing boundary conditions as well as an inhomogeneous source term<br />
in order to obtain a stationary flow of condensate through the guide. We<br />
show that the nonlinear interaction between the atoms leads to a significant<br />
modification of the positions and shapes of the resonance peaks as<br />
compared to the noninteracting case.<br />
[1] H. Ott et al., Phys. Rev. Lett. 87, 230401 (2001); J. Schmiedmayer et<br />
al., J. Mod. Optics 47, 2789 (2000); W. Hänsel et al., Nature 413, 498<br />
(1999).<br />
[2] J. Fortagh and C. Zimmermann, Physik Journal, Juni 2003