2,857 research outputs found
Nonequilibrium Green's Function Approach to Phonon Transport in Defective Carbon Nanotubes
We have developed a new theoretical formalism for phonon transport in
nanostructures using the nonequilibrium phonon Green's function technique and
have applied it to thermal conduction in defective carbon nanotubes. The
universal quantization of low-temperature thermal conductance in carbon
nanotubes can be observed even in the presence of local structural defects such
as vacancies and Stone-Wales defects, since the long wavelength acoustic
phonons are not scattered by local defects. At room temperature, however,
thermal conductance is critically affected by defect scattering since incident
phonons are scattered by localized phonons around the defects. We find a
remarkable change from quantum to classical features for the thermal transport
through defective CNTs with increasing temperature.Comment: 5 pages, 3 figures, accepted for publication in Phys. Rev. Let
Beam polarization effects on top-pair production at the ILC
Full one-loop electroweak-corrections for an
process associated with sequential decay are
discussed. At the one-loop level, the spin-polarization effects of the initial
electron and positron beams are included in the total and differential cross
sections. A narrow-width approximation is used to treat the top-quark
production and decay while including full spin correlations between them. We
observed that the radiative corrections due to the weak interaction have a
large polarization dependence on both the total and differential cross
sections. Therefore, experimental observables that depend on angular
distributions such as the forward-backward asymmetry of the top production
angle must be treated carefully including radiative corrections. We also
observed that the energy distribution of bottom quarks is majorly affected by
the radiative corrections.Comment: 15 pages, 8 figure
Geometrical Pumping in Quantum Transport: Quantum Master Equation Approach
For an open quantum system, we investigate the pumped current induced by a
slow modulation of control parameters on the basis of the quantum master
equation and full counting statistics. We find that the average and the
cumulant generating function of the pumped quantity are characterized by the
geometrical Berry-phase-like quantities in the parameter space, which is
associated with the generator of the master equation. From our formulation, we
can discuss the geometrical pumping under the control of the chemical
potentials and temperatures of reservoirs. We demonstrate the formulation by
spinless electrons in coupled quantum dots. We show that the geometrical
pumping is prohibited for the case of non-interacting electrons if we modulate
only temperatures and chemical potentials of reservoirs, while the geometrical
pumping occurs in the presence of an interaction between electrons
Quantum Electrodynamics at Large Distances III: Verification of Pole Factorization and the Correspondence Principle
In two companion papers it was shown how to separate out from a scattering
function in quantum electrodynamics a distinguished part that meets the
correspondence-principle and pole-factorization requirements. The integrals
that define the terms of the remainder are here shown to have singularities on
the pertinent Landau singularity surface that are weaker than those of the
distinguished part. These remainder terms therefore vanish, relative to the
distinguished term, in the appropriate macroscopic limits. This shows, in each
order of the perturbative expansion, that quantum electrodynamics does indeed
satisfy the pole-factorization and correspondence-principle requirements in the
case treated here. It also demonstrates the efficacy of the computational
techniques developed here to calculate the consequences of the principles of
quantum electrodynamics in the macroscopic and mesoscopic regimes.Comment: latex, 39 pages, 2 Figures included as uuencoded, tarred, gzipped,
encapsulated postscript files, uses math_macros.te
Topological Floquet-Thouless energy pump
We explore adiabatic pumping in the presence of periodic drive, finding a new
phase in which the topologically quantized pumped quantity is energy rather
than charge. The topological invariant is given by the winding number of the
micromotion with respect to time within each cycle, momentum, and adiabatic
tuning parameter. We show numerically that this pump is highly robust against
both disorder and interactions, breaking down at large values of either in a
manner identical to the Thouless charge pump. Finally, we suggest experimental
protocols for measuring this phenomenon.Comment: 4 pages, 4 figures. Minor replacements and references adde
Generalized Jarzynski Equality under Nonequilibrium Feedback Control
The Jarzynski equality is generalized to situations in which nonequilibrium
systems are subject to a feedback control. The new terms that arise as a
consequence of the feedback describe the mutual information content obtained by
measurement and the efficacy of the feedback control. Our results lead to a
generalized fluctuation-dissipation theorem that reflects the readout
information, and can be experimentally tested using small thermodynamic
systems. We illustrate our general results by an introducing "information
ratchet," which can transport a Brownian particle in one direction and extract
a positive work from the particle
Quantum-number projection in the path-integral renormalization group method
We present a quantum-number projection technique which enables us to exactly
treat spin, momentum and other symmetries embedded in the Hubbard model. By
combining this projection technique, we extend the path-integral
renormalization group method to improve the efficiency of numerical
computations. By taking numerical calculations for the standard Hubbard model
and the Hubbard model with next nearest neighbor transfer, we show that the
present extended method can extremely enhance numerical accuracy and that it
can handle excited states, in addition to the ground state.Comment: 11 pages, 7 figures, submitted to Phys. Rev.
Hamiltonian Derivations of the Generalized Jarzynski Equalities under Feedback Control
In the presence of feedback control by "Maxwell's demon," the second law of
thermodynamics and the nonequilibrium equalities such as the Jarzynski equality
need to be generalized. In this paper, we derive the generalized Jarzynski
equalities for classical Hamiltonian dynamics based on the Liouville's theorem,
which is the same approach as the original proof of the Jarzynski equality
[Phys. Rev. Lett. 78, 2690 (1997)]. The obtained equalities lead to the
generalizations of the second law of thermodynamics for the Hamiltonian systems
in the presence of feedback control.Comment: Proceedings of "STATPHYS - Kolkata VII", November 26-30, 2010,
Kolkata, Indi
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