14,374 research outputs found
Non-dissipative Thermal Transport and Magnetothermal Effect for the Spin-1/2 Heisenberg Chain
Anomalous magnetothermal effects are discussed in the spin-1/2 Heisenberg
chain. The energy current is related to one of the non-trivial conserved
quantities underlying integrability and therefore both the diagonal and off
diagonal dynamical correlations of spin and energy current diverge. The
energy-energy and spin-energy current correlations at finite temperatures are
exactly calculated by a lattice path integral formulation. The low-temperature
behavior of the thermomagnetic (magnetic Seebeck) coefficient is also
discussed. Due to effects of strong correlations, we observe the magnetic
Seebeck coefficient changes sign at certain interaction strengths and magnetic
fields.Comment: 4 pages, references added, typos corrected, Conference proceedings of
SPQS 2004, Sendai, Japa
Low-temperature transport in Heisenberg chains
A technique to determine accurately transport properties of integrable and
non-integrable quantum-spin chains at finite temperatures by Quantum
Monte-Carlo is presented. The reduction of the Drude weight by interactions in
the integrable gapless regime is evaluated. Evidence for the absence of a Drude
weight in the gapless regime of a non-integrable system with longer-ranged
interactions is presented. We estimate the effect of the non-integrability on
the transport properties and compare with recent experiments on one-dimensional
quantum-spin chains.Comment: accepted for publication (PRL
Memory and nonlocal effects in heat transport : from diffusive to ballistic regimes
The authors discuss a generalized transportmodel including memory and nonlocal effects, which aims to describe the transition of heat transport from the diffusive regime to the ballistic regime. By using an effective thermal conductivity depending on the Knudsen number, they describe in a single equation the behavior of conductivity in terms of the system size and a reduction in the limit flux through nanoscale devices
Two classes of nonlocal Evolution Equations related by a shared Traveling Wave Problem
We consider reaction-diffusion equations and Korteweg-de Vries-Burgers (KdVB)
equations, i.e. scalar conservation laws with diffusive-dispersive
regularization. We review the existence of traveling wave solutions for these
two classes of evolution equations. For classical equations the traveling wave
problem (TWP) for a local KdVB equation can be identified with the TWP for a
reaction-diffusion equation. In this article we study this relationship for
these two classes of evolution equations with nonlocal diffusion/dispersion.
This connection is especially useful, if the TW equation is not studied
directly, but the existence of a TWS is proven using one of the evolution
equations instead. Finally, we present three models from fluid dynamics and
discuss the TWP via its link to associated reaction-diffusion equations
Thermomagnetic Power and Figure of Merit for Spin-1/2 Heisenberg Chain
Transport properties in the presence of magnetic fields are numerically
studied for the spin-1/2 Heisenberg XXZ chain. The breakdown of the
spin-reversal symmetry due to the magnetic field induces the magnetothermal
effect. In analogy with the thermoelectric effect in electron systems, the
thermomagnetic power (magnetic Seebeck coefficient) is provided, and is
numerically evaluated by the exact diagonalization for wide ranges of
temperatures and various magnetic fields. For the antiferromagnetic regime, we
find the magnetic Seebeck coefficient changes sign at certain temperatures,
which is interpreted as an effect of strong correlations. We also compute the
thermomagnetic figure of merit determining the efficiency of the thermomagnetic
devices for cooling or power generation.Comment: 8 page
Bergman Kernel from Path Integral
We rederive the expansion of the Bergman kernel on Kahler manifolds developed
by Tian, Yau, Zelditch, Lu and Catlin, using path integral and perturbation
theory, and generalize it to supersymmetric quantum mechanics. One physics
interpretation of this result is as an expansion of the projector of wave
functions on the lowest Landau level, in the special case that the magnetic
field is proportional to the Kahler form. This is relevant for the quantum Hall
effect in curved space, and for its higher dimensional generalizations. Other
applications include the theory of coherent states, the study of balanced
metrics, noncommutative field theory, and a conjecture on metrics in black hole
backgrounds. We give a short overview of these various topics. From a
conceptual point of view, this expansion is noteworthy as it is a geometric
expansion, somewhat similar to the DeWitt-Seeley-Gilkey et al short time
expansion for the heat kernel, but in this case describing the long time limit,
without depending on supersymmetry.Comment: 27 page
Conductivity of quantum-spin chains: A Quantum Monte Carlo approach
We discuss zero-frequency transport properties of various spin-1/2 chains. We
show, that a careful analysis of Quantum Monte-Carlo (QMC) data on the
imaginary axis allows to distinguish between intrinsic ballistic and diffusive
transport. We determine the Drude weight, current-relaxation life-time and the
mean-free path for integrable and a non-integrable quantum-spin chain. We
discuss, in addition, some phenomenological relations between various
transport-coefficients and thermal response functions
SYMPA, a dedicated instrument for Jovian Seismology. II. Real performance and first results
Context. Due to its great mass and its rapid formation, Jupiter has played a
crucial role in shaping the Solar System. The knowledge of its internal
structure would strongly constrain the solar system formation mechanism.
Seismology is the most efficient way to probe directly the internal structure
of giant planets. Aims. SYMPA is the first instrument dedicated to the
observations of free oscillations of Jupiter. Principles and theoretical
performance have been presented in paper I. This second paper describes the
data processing method, the real instrumental performance and presents the
first results of a Jovian observation run, lead in 2005 at Teide Observatory.
Methods. SYMPA is a Fourier transform spectrometer which works at fixed optical
path difference. It produces Doppler shift maps of the observed object.
Velocity amplitude of Jupiter's oscillations is expected below 60 cm/s. Results
Despite light technical defects, the instrument demonstrated to work correctly,
being limited only by photon noise, after a careful analysis. A noise level of
about 12 cm/s has been reached on a 10-night observation run, with 21 % duty
cycle, which is 5 time better than previous similar observations. However, no
signal from Jupiter is clearly highlighted.Comment: 13 pages, 26 figure
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