21,936 research outputs found
Dynamical recovery of SU(2) symmetry in the mass-quenched Hubbard model
We use non-equilibrium dynamical mean-field theory with iterative
perturbation theory as an impurity solver to study the recovery of
symmetry in real-time following a hopping integral parameter quench from a
mass-imbalanced to a mass-balanced single-band Hubbard model at half-filling. A
dynamical order parameter is defined to characterize the evolution
of the system towards symmetry. By comparing the momentum dependent
occupation from an equilibrium calculation (with the symmetric
Hamiltonian after the quench at an effective temperature) with the data from
our non-equilibrium calculation, we conclude that the symmetry
recovered state is a thermalized state. Further evidence from the evolution of
the density of states supports this conclusion. At the same time, we find the
order parameter in the weak Coulomb interaction regime undergoes an approximate
exponential decay. We numerically investigate the interplay of the relevant
parameters (initial temperature, Coulomb interaction strength, initial
mass-imbalance ratio) and their combined effect on the thermalization behavior.
Finally, we study evolution of the order parameter as the hopping parameter is
changed with either a linear ramp or a pulse. Our results can be useful in
strategies to engineer the relaxation behavior of interacting, quantum
many-particle systems.Comment: 8 pages, 6 figure
The limit behavior of the evolution of Tsallis entropy in self-gravitating systems
In this letter, we study the limit behavior of the evolution of Tsallis
entropy in self-gravitating systems. The study is carried out under two
different situations, drawing the same conclusion. No matter in the energy
transfer process or in the mass transfer process inside the system, when
nonextensive parameter q is more than unity, the total entropy is bounded; on
the contrary, when this parameter is less than unity, the total entropy is
unbounded. There are proofs in both theory and observation that the q is always
more than unity. So the Tsallis entropy in self-gravitating system generally
exhibits a bounded property. This indicates the existence of global maximum of
Tsallis entropy. It is possible for self-gravitating systems to evolve to
thermodynamically stable states
Penalized variable selection procedure for Cox models with semiparametric relative risk
We study the Cox models with semiparametric relative risk, which can be
partially linear with one nonparametric component, or multiple additive or
nonadditive nonparametric components. A penalized partial likelihood procedure
is proposed to simultaneously estimate the parameters and select variables for
both the parametric and the nonparametric parts. Two penalties are applied
sequentially. The first penalty, governing the smoothness of the multivariate
nonlinear covariate effect function, provides a smoothing spline ANOVA
framework that is exploited to derive an empirical model selection tool for the
nonparametric part. The second penalty, either the
smoothly-clipped-absolute-deviation (SCAD) penalty or the adaptive LASSO
penalty, achieves variable selection in the parametric part. We show that the
resulting estimator of the parametric part possesses the oracle property, and
that the estimator of the nonparametric part achieves the optimal rate of
convergence. The proposed procedures are shown to work well in simulation
experiments, and then applied to a real data example on sexually transmitted
diseases.Comment: Published in at http://dx.doi.org/10.1214/09-AOS780 the Annals of
Statistics (http://www.imstat.org/aos/) by the Institute of Mathematical
Statistics (http://www.imstat.org
Metal-insulator transition in three-band Hubbard model with strong spin-orbit interaction
Recent investigations suggest that both spin-orbit coupling and electron
correlation play very crucial roles in the transition metal oxides. By
using the generalized Gutzwiller variational method and dynamical mean-field
theory with the hybridization expansion continuous time quantum Monte Carlo as
impurity solver, the three-band Hubbard model with full Hund's rule coupling
and spin-orbit interaction terms, which contains the essential physics of
partially filled sub-shell of materials, is studied
systematically. The calculated phase diagram of this model exhibits three
distinct phase regions, including metal, band insulator and Mott insulator
respectively. We find that the spin-orbit coupling term intends to greatly
enhance the tendency of the Mott insulator phase. Furthermore, the influence of
the electron-electron interaction on the effective strength of spin-orbit
coupling in the metallic phase is studied in detail. We conclude that the
electron correlation effect on the effective spin-orbit coupling is far beyond
the mean-field treatment even in the intermediate coupling region.Comment: 8 pages, 8 figure
Floquet band structure of a semi-Dirac system
In this work we use Floquet-Bloch theory to study the influence of circularly
and linearly polarized light on two-dimensional band structures with semi-Dirac
band touching points, taking the anisotropic nearest neighbor hopping model on
the honeycomb lattice as an example. We find circularly polarized light opens a
gap and induces a band inversion to create a finite Chern number in the
two-band model. By contrast, linearly polarized light can either open up a gap
(polarized in the quadratically dispersing direction) or split the semi-Dirac
band touching point into two Dirac points (polarized in the linearly dispersing
direction) by an amount that depends on the amplitude of the light. Motivated
by recent pump-probe experiments, we investigated the non-equilibrium spectral
properties and momentum-dependent spin-texture of our model in the Floquet
state following a quench in absence of phonons, and in the presence of phonon
dissipation that leads to a steady-state independent of the pump protocol.
Finally, we make connections to optical measurements by computing the frequency
dependence of the longitudinal and transverse optical conductivity for this
two-band model. We analyze the various contributions from inter-band
transitions and different Floquet modes. Our results suggest strategies for
optically controlling band structures and experimentally measuring topological
Floquet systems.Comment: 17 pages, 8 figure
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