15,293 research outputs found
Devil's staircase of incompressible electron states in a nanotube
It is shown that a periodic potential applied to a nanotube can lock
electrons into incompressible states. Depending on whether electrons are weakly
or tightly bound to the potential, excitation gaps open up either due to the
Bragg diffraction enhanced by the Tomonaga - Luttinger correlations, or via
pinning of the Wigner crystal. Incompressible states can be detected in a
Thouless pump setup, in which a slowly moving periodic potential induces
quantized current, with a possibility to pump on average a fraction of an
electron per cycle as a result of interactions.Comment: 4 pages, 1 figure, published versio
Strong Evidence of Normal Heat Conduction in a one-Dimensional Quantum System
We investigate how the normal energy transport is realized in one-dimensional
quantum systems using a quantum spin system. The direct investigation of local
energy distribution under thermal gradient is made using the quantum master
equation, and the mixing properties and the convergence of the Green-Kubo
formula are investigated when the number of spin increases. We find that the
autocorrelation function in the Green-Kubo formula decays as to
a finite value which vanishes rapidly with the increase of the system size. As
a result, the Green-Kubo formula converges to a finite value in the
thermodynamic limit. These facts strongly support the realization of Fourier
heat law in a quantum system.Comment: 7 pages 6 figure
Energy Dissipation and Fluctuation-Response in Driven Quantum Langevin Dynamics
Energy dissipation in a nonequilibrium steady state is studied in driven
quantum Langevin systems. We study energy dissipation flow to thermal
environment, and obtain a general formula for the average rate of energy
dissipation using an autocorrelation function for the system variable. This
leads to a general expression of the equality that connects the violation of
the fluctuation-response relation to the rate of energy dissipation, the
classical version of which was first studied by Harada and Sasa. We also point
out that the expression depends on coupling form between system and reservoir.Comment: 4 pages, 1 figur
Elastic scattering theory and transport in graphene
Electron properties of graphene are described in terms of Dirac fermions.
Here we thoroughly outline the elastic scattering theory for the
two-dimensional massive Dirac fermions in the presence of an axially symmetric
potential. While the massless limit is relevant for pristine graphene, keeping
finite mass allows for generalizations onto situations with broken symmetry
between the two sublattices, and provides a link to the scattering theory of
electrons in a parabolic band. We demonstrate that the Dirac theory requires
short-distance regularization for potentials which are more singular than 1/r.
The formalism is then applied to scattering off a smooth short-ranged
potential. Next we consider the Coulomb potential scattering, where the Dirac
theory is consistent for a point scatterer only for the effective impurity
strength below 1/2. From the scattering phase shifts we obtain the exact
Coulomb transport cross-section in terms of the impurity strength. The results
are relevant for transport in graphene in the presence of impurities that do
not induce scattering between the Dirac points in the Brillouin zone.Comment: 17 pages, 4 figures. Published versio
Enhancement of the transverse non-reciprocal magneto-optical effect
The origin and properties of the transverse non-reciprocal magneto-optical
(nMO) effect were studied. The transverse nMO effect occurs in the case when
light propagates perpendicularly to the magnetic field. It was demonstrated
that light can experience the transverse nMO effect only when it propagates in
the vicinity of a boundary between two materials and the optical field at least
in one material is evanescent. The transverse nMO effect is pronounced in the
cases of surface plasmons and waveguiding modes. The magnitude of the
transverse nMO effect is comparable to or greater than the magnitude of the
longitudinal nMO effect. In the case of surface plasmons propagating at a
boundary between the transition metal and the dielectric it is possible to
magnify the transverse nMO effect and the magneto-optical figure-of-merit may
increase from a few percents to above 100%. The scalar dispersion relation,
which describes the transverse MO effect in cases of waveguide modes and
surface plasmons propagating in a multilayer MO slab, was derived
Low frequency Rabi spectroscopy for a dissipative two-level system
We have analyzed the interaction of a dissipative two level quantum system
with high and low frequency excitation. The system is continuously and
simultaneously irradiated by these two waves. If the frequency of the first
signal is close to the level separation the response of the system exhibits
undamped low frequency oscillations whose amplitude has a clear resonance at
the Rabi frequency with the width being dependent on the damping rates of the
system. The method can be useful for low frequency Rabi spectroscopy in various
physical systems which are described by a two level Hamiltonian, such as nuclei
spins in NMR, double well quantum dots, superconducting flux and charge qubits,
etc. As the examples, the application of the method to a nuclear spin and to
the readout of a flux qubit are briefly discussed.Comment: 4 pages, 3 figures, the figures are modifie
Electron properties of carbon nanotubes in a periodic potential
A periodic potential applied to a nanotube is shown to lock electrons into
incompressible states that can form a devil's staircase. Electron interactions
result in spectral gaps when the electron density (relative to a half-filled
Carbon pi-band) is a rational number per potential period, in contrast to the
single-particle case where only the integer-density gaps are allowed. When
electrons are weakly bound to the potential, incompressible states arise due to
Bragg diffraction in the Luttinger liquid. Charge gaps are enhanced due to
quantum fluctuations, whereas neutral excitations are governed by an effective
SU(4)~O(6) Gross-Neveu Lagrangian. In the opposite limit of the tightly bound
electrons, effects of exchange are unimportant, and the system behaves as a
single fermion mode that represents a Wigner crystal pinned by the external
potential, with the gaps dominated by the Coulomb repulsion. The phase diagram
is drawn using the effective spinless Dirac Hamiltonian derived in this limit.
Incompressible states can be detected in the adiabatic transport setup realized
by a slowly moving potential wave, with electron interactions providing the
possibility of pumping of a fraction of an electron per cycle (equivalently, in
pumping at a fraction of the base frequency).Comment: 21 pgs, 8 fig
One-loop calculations of hyperon polarizabilities under the large N_c consistency condition
The spin-averaged electromagnetic polarizabilities of the hyperons
and are calculated within the one-loop approximation by use of the
dispersion theory. The photon and meson couplings to hyperons are determined so
as to satisfy the large N_c consistency condition. It is shown that in order
for the large N_c consistency condition to hold exotic hyperon states such as
with I=2 and J=3/2 are required in the calculation of the
magnetic polarizability of the state.Comment: 17 pages, REVTeX, no figure
Model for hypernucleus production in heavy ion collisions
We estimate the production cross sections of hypernuclei in projectile like
fragment (PLF) in heavy ion collisions. The discussed scenario for the
formation cross section of hypernucleus is: (a) Lambda particles are produced
in the participant region but have a considerable rapidity spread and (b)
Lambda with rapidity close to that of the PLF and total momentum (in the rest
system of PLF) up to Fermi motion can then be trapped and produce hypernuclei.
The process (a) is considered here within Heavy Ion Jet Interacting Generator
HIJING-BBbar model and the process (b) in the canonical thermodynamic model
(CTM). We estimate the production cross-sections for light hypernuclei for C +
C at 3.7 GeV total nucleon-nucleon center of mass energy and for Ne+Ne and
Ar+Ar collisions at 5.0 GeV. By taking into account explicitly the impact
parameter dependence of the colliding systems, it is found that the cross
section is different from that predicted by the coalescence model and large
discrepancy is obtained for 6_He and 9_Be hypernuclei.Comment: 9 pages, 4 figures, 3 tables, revtex4, added reference
Asymmetric Heat Flow in Mesoscopic Magnetic System
The characteristics of heat flow in a coupled magnetic system are studied.
The coupled system is composed of a gapped chain and a gapless chain. The
system size is assumed to be quite small so that the mean free path is
comparable to it. When the parameter set of the temperatures of reservoirs is
exchanged, the characteristics of heat flow are studied with the Keldysh Green
function technique. The asymmetry of current is found in the presence of a
local equilibrium process at the contact between the magnetic systems. The
present setup is realistic and such an effect will be observed in real
experiments. We also discuss the simple phenomenological explanation to obtain
the asymmetry.Comment: 13 pages, 3 figure
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