2,064 research outputs found
Phonon-mediated electron spin phase diffusion in a quantum dot
An effective spin relaxation mechanism that leads to electron spin
decoherence in a quantum dot is proposed. In contrast to the common
calculations of spin-flip transitions between the Kramers doublets, we take
into account a process of phonon-mediated fluctuation in the electron spin
precession and subsequent spin phase diffusion. Specifically, we consider
modulations in the longitudinal g-factor and hyperfine interaction induced by
the phonon-assisted transitions between the lowest electronic states. Prominent
differences in the temperature and magnetic field dependence between the
proposed mechanisms and the spin-flip transitions are expected to facilitate
its experimental verification. Numerical estimation demonstrates highly
efficient spin relaxation in typical semiconductor quantum dots.Comment: 5 pages, 1 figur
Growing length and time scales in a suspension of athermal particles
We simulate a relaxation process of non-brownian particles in a sheared
viscous medium; the small shear strain is initially applied to a system, which
then undergoes relaxation. The relaxation time and the correlation length are
estimated as functions of density, which algebraically diverge at the jamming
density. This implies that the relaxation time can be scaled by the correlation
length using the dynamic critical exponent, which is estimated as 4.6(2). It is
also found that shear stress undergoes power-law decay at the jamming density,
which is reminiscent of critical slowing down
Non-equilibrium statistical mechanics of classical nuclei interacting with the quantum electron gas
Kinetic equations governing time evolution of positions and momenta of atoms
in extended systems are derived using quantum-classical ensembles within the
Non-Equilibrium Statistical Operator Method (NESOM). Ions are treated
classically, while their electrons quantum mechanically; however, the
statistical operator is not factorised in any way and no simplifying
assumptions are made concerning the electronic subsystem. Using this method, we
derive kinetic equations of motion for the classical degrees of freedom (atoms)
which account fully for the interaction and energy exchange with the quantum
variables (electrons). Our equations, alongside the usual Newtonian-like terms
normally associated with the Ehrenfest dynamics, contain additional terms,
proportional to the atoms velocities, which can be associated with the
electronic friction. Possible ways of calculating the friction forces which are
shown to be given via complicated non-equilibrium correlation functions, are
discussed. In particular, we demonstrate that the correlation functions are
directly related to the thermodynamic Matsubara Green's functions, and this
relationship allows for the diagrammatic methods to be used in treating
electron-electron interaction perturbatively when calculating the correlation
functions. This work also generalises previous attempts, mostly based on model
systems, of introducing the electronic friction into Molecular Dynamics
equations of atoms.Comment: 18 page
A Green's function decoupling scheme for the Edwards fermion-boson model
Holes in a Mott insulator are represented by spinless fermions in the
fermion-boson model introduced by Edwards. Although the physically interesting
regime is for low to moderate fermion density the model has interesting
properties over the whole density range. It has previously been studied at
half-filling in the one-dimensional (1D) case by numerical methods, in
particular exact diagonalization and density matrix renormalization group
(DMRG). In the present study the one-particle Green's function is calculated
analytically by means of a decoupling scheme for the equations of motion, valid
for arbitrary density in 1D, 2D and 3D with fairly large boson energy and zero
boson relaxation parameter. The Green's function is used to compute some ground
state properties, and the one-fermion spectral function, for fermion densities
n=0.1, 0.5 and 0.9 in the 1D case. The results are generally in good agreement
with numerical results obtained by DMRG and dynamical DMRG and new light is
shed on the nature of the ground state at different fillings. The Green's
function approximation is sufficiently successful in 1D to justify future
application to the 2D and 3D cases.Comment: 19 pages, 7 figures, final version with updated reference
Gauge invariant dressed holon and spinon in doped cuprates
We develop a partial charge-spin separation fermion-spin theory implemented
the gauge invariant dressed holon and spinon. In this novel approach, the
physical electron is decoupled as the gauge invariant dressed holon and spinon,
with the dressed holon behaviors like a spinful fermion, and represents the
charge degree of freedom together with the phase part of the spin degree of
freedom, while the dressed spinon is a hard-core boson, and represents the
amplitude part of the spin degree of freedom, then the electron single
occupancy local constraint is satisfied. Within this approach, the charge
transport and spin response of the underdoped cuprates is studied. It is shown
that the charge transport is mainly governed by the scattering from the dressed
holons due to the dressed spinon fluctuation, while the scattering from the
dressed spinons due to the dressed holon fluctuation dominates the spin
response.Comment: 8 pages, Revtex, three figures are include
Tuning the Non-local Spin-Spin Interaction between Quantum Dots with a Magnetic Field
We describe a device where the non-local spin-spin interaction between two
quantum dots can be turned on and off and even changed sign with a very small
magnetic field. The setup consists of two quantum dots at the edge of two
two-dimensional electron gases (2DEGs). The quantum dots' spins are coupled
through a RKKY-like interaction mediated by the electrons in the 2DEGs. A small
magnetic field perpendicular to the plane of the 2DEG is used as a tuning
parameter. When the cyclotron radius is commensurate with the interdot
distance, the spin-spin interaction is amplified by a few orders of magnitude.
The sign of the interaction is controlled by finely tuning the magnetic field.
Our setup allows for several dots to be coupled in a linear arrangement and it
is not restricted to nearest-neighbors interaction.Comment: 4 pages, 5 figures. Published versio
Calculation of shear viscosity using Green-Kubo relations within a parton cascade
The shear viscosity of a gluon gas is calculated using the Green-Kubo
relation. Time correlations of the energy-momentum tensor in thermal
equilibrium are extracted from microscopic simulations using a parton cascade
solving various Boltzmann collision processes. We find that the pQCD based
gluon bremsstrahlung described by Gunion-Bertsch processes significantly lowers
the shear viscosity by a factor of 3-8 compared to elastic scatterings. The
shear viscosity scales with the coupling as 1/(alpha_s^2\log(1/alpha_s)). For a
constant coupling constant the shear viscosity to entropy density ratio has no
dependence on temperature. Replacing the pQCD-based collision angle
distribution of binary scatterings by an isotropic form decreases the shear
viscosity by a factor of 3.Comment: 17 pages, 5 figure
The Steady State Distribution of the Master Equation
The steady states of the master equation are investigated. We give two
expressions for the steady state distribution of the master equation a la the
Zubarev-McLennan steady state distribution, i.e., the exact expression and an
expression near equilibrium. The latter expression obtained is consistent with
recent attempt of constructing steady state theormodynamics.Comment: 6 pages, No figures. A mistake was correcte
Dynamics of the Free Surface of a Conducting Liquid in a Near-Critical Electric Field
Near-critical behavior of the free surface of an ideally conducting liquid in
an external electric field is considered. Based on an analysis of three-wave
processes using the method of integral estimations, sufficient criteria for
hard instability of a planar surface are formulated. It is shown that the
higher-order nonlinearities do not saturate the instability, for which reason
the growth of disturbances has an explosive character.Comment: 19 page
A temperature behavior of the frustrated translational mode of adsorbate and the nature of the "adsorbate-substrate" interaction
A temperature behavior of the frustrated translational mode (T-mode) of a
light particle, coupled by different regimes of ohmicity to the surface, is
studied within a formalism of the generalized diffusion coefficients. The
memory effects of the adsorbate motion are considered to be the main reason of
the T-mode origin. Numerical calculations yield a thermally induced shift and
broadening of the T-mode, which is found to be linear in temperature for Ohmic
and super-Ohmic systems and nonlinear for strongly sub-Ohmic ones. We obtain
analytical expressions for the T-mode shift and width at weak coupling for the
systems with integer "ohmicity" indexes n=0-2 in zero temperature and high
temperature limits. We provide an explanation of the experimentally observed
blue- or red-shifts of the T-mode on the basis of a comparative analysis of two
typical times of the system evolution: a time of decay of the
"velocity-velocity" autocorrelation function, and a correlation time of the
thermal bath random forces. A relation of the T-mode to the multiple jumps of
the adsorbate is discussed, and generalization of conditions of the multiple
hopping to the case of quantum surface diffusion is performed.Comment: 12 pages, 4 figure
- …