426 research outputs found
Kinetic theory of nonlinear diffusion in a weakly disordered nonlinear Schr\"odinger chain in the regime of homogeneous chaos
We study the discrete nonlinear Schr\"oinger equation with weak disorder,
focusing on the regime when the nonlinearity is, on the one hand, weak enough
for the normal modes of the linear problem to remain well resolved, but on the
other, strong enough for the dynamics of the normal mode amplitudes to be
chaotic for almost all modes. We show that in this regime and in the limit of
high temperature, the macroscopic density satisfies the nonlinear
diffusion equation with a density-dependent diffusion coefficient,
. An explicit expression for is obtained in terms of
the eigenfunctions and eigenvalues of the linear problem, which is then
evaluated numerically. The role of the second conserved quantity (energy) in
the transport is also quantitatively discussed.Comment: 24 pages, 13 figure
Theory of electron spin resonance in bulk topological insulators Bi2Se3, Bi2Te3 and Sb2Te3
We report a theoretical study of electron spin resonance in bulk topological
insulators, such as Bi2Se3, Bi2Te3 and Sb2Te3. Using the effective four-band
model, we find the electron energy spectrum in a static magnetic field and
determine the response to electric and magnetic dipole perturbations,
represented by oscillating electric and magnetic fields perpendicular to the
static field. We determine the associated selection rules and calculate the
absorption spectra. This enables us to separate the effective orbital and spin
degrees of freedom and to determine the effective g-factors for electrons and
holes.Comment: 10 pages, 4 figure
Effect of inelastic collisions on multiphonon Raman scattering in graphene
We calculate the probabilities of two- and four-phonon Raman scattering in
graphene and show how the relative intensities of the overtone peaks encode
information about relative rates of different inelastic processes electrons are
subject to. If the most important processes are electron-phonon and
electron-electron scattering, the rate of the latter can be deduced from the
Raman spectra
Effect of disorder on coherent quantum phase slips in Josephson junction chains
We study coherent quantum phase-slips in a Josephson junction chain,
including two types of quenched disorder: random spatial modulation of the
junction areas and random induced background charges. Usually, the quantum
phase-slip amplitude is sensitive to the normal mode structure of
superconducting phase oscillations in the ring (Mooij-Sch\"on modes, which are
all localized by the area disorder). However, we show that the modes'
contribution to the disorder-induced phase-slip action fluctuations is small,
and the fluctuations of the action on different junctions are mainly determined
by the local junction parameters. We study the statistics of the total QPS
amplitude on the chain and show that it can be non-Gaussian for not
sufficiently long chains
Dissipation in a superconducting artificial atom due to a single non-equilibrium quasiparticle
We study a superconducting artificial atom which is represented by a single
Josephson junction or a Josephson junction chain, capacitively coupled to a
coherently driven transmission line, and which contains exactly one residual
quasiparticle (or up to one quasiparticle per island in a chain). We study the
dissipation in the atom induced by the quasiparticle tunneling, taking into
account the quasiparticle heating by the drive. We calculate the transmission
coefficient in the transmission line for drive frequencies near resonance and
show that, when the artificial atom spectrum is nearly harmonic, the intrinsic
quality factor of the resonance increases with the drive power. This
counterintuitive behavior is due to the energy dependence of the quasiparticle
density of states
Exciton-phonon relaxation bottleneck and radiative decay of thermal exciton reservoir in two-dimensional materials
We study exciton radiative decay in a two-dimensional material, taking into
account large thermal population in the non-radiative states, from which
excitons are scattered into the radiative states by acoustic phonons. We find
an analytical solution of the kinetic equation for the non-equilibrium
distribution function of excitons in the radiative states. Our estimates for
bright excitons in transition metal dichalcogenides indicate a strong depletion
of radiative state population due to insufficient exciton-phonon scattering
rate at low temperatures.Comment: 8 pages, 4 figure
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