arXiv subjects

Hua-Tong Yang

Publications and source records attributed to Hua-Tong Yang.

6 recordsLinked to original sources

arXiv2024

Cusps in the quench dynamics of a Bloch state

We report some nonsmooth dynamics of a Bloch state in a one-dimensional tight binding model with the periodic boundary condition. After a sudden change of the potential of an arbitrary site, quantities like the survival probability of the particle in the initial Bloch state show cusps periodically, with the period being the Heisenberg time associated with the energy spectrum. This phenomenon is a \emph{nonperturbative} counterpart of the nonsmooth dynamics observed previously (Zhang and Haque, arXiv:1404.4280) in a periodically driven tight binding model. Underlying the cusps is an exactly solvable model, which consists of equally spaced levels extending from $-\infty$ to $+\infty $, between which two arbitrary levels are coupled to each other by the same strength.

quant-ph↗

arXiv2016

Sudden jumps and plateaus in the quench dynamics of a Bloch state

We take a one-dimensional tight binding chain with periodic boundary condition and put a particle in an arbitrary Bloch state, then quench it by suddenly changing the potential of an arbitrary site. In the ensuing time evolution, the probability density of the wave function at an arbitrary site \emph{jumps indefinitely between plateaus}. This phenomenon adds to a former one in which the survival probability of the particle in the initial Bloch state shows \emph{cusps} periodically, which was found in the same scenario [Zhang J. M. and Yang H.-T., EPL, \textbf{114} (2016) 60001]. The plateaus support the scattering wave picture of the quench dynamics of the Bloch state. Underlying the cusps and jumps is the exactly solvable, nonanalytic dynamics of a Luttinger-like model, based on which, the locations of the jumps and the heights of the plateaus are accurately predicted.

cond-mat.quant-gas↗

arXiv2012

Potential-driven eddy current in rippled graphene nanoribbons

It is well known that an eddy current will be induced in a conductor subject to a varying magnetic field. Here we propose another mechanism of generating nano-scale eddy current in rippled graphene nanoribbons(GNRs), which is only driven by an electric potential. In particular, it is found that under appropriate gate voltages, a local deformation may induce some unexpected global eddy currents, which form vortices in both rippled and entire flat areas of the GNR. We will explain that these vortices in flat areas is a manifestation of the nonlocality of quantum interference.

cond-mat.mes-hall↗

arXiv2010

Shift of Dirac points and strain induced pseudo-magnetic field in graphene

We propose that the strain induced effective pseudo-magnetic field in graphene can also be explained by a curl movement of the Dirac points, if the Dirac points can be regarded as a slowly varying function of position. We also prove that the Dirac points must be confined within two triangles, each one has 1/8 the area of the Brillouin zone.

cond-mat.mes-hall↗

arXiv2007

Description of spin transport and precession in spin-orbit coupling systems and a general equation of continuity

By generalizing the usual current density to a matrix with respect to spin variables, a general equation of continuity satisfied by the density matrix and current density matrix has been derived. This equation holds in arbitrary spin-orbit coupling systems as long as its Hamiltonian can be expressed in terms of a power series in momentum. Thereby, the expressions of the current density matrix and a torque density matrix are obtained. The current density matrix completely describes both the usual current and spin current as well; while the torque density matrix describes the spin precession caused by a total effective magnetic field, which may include a realistic and an effective one due to the spin-orbit coupling. In contrast to the conventional definition of spin current, this expression contains an additional term if the Hamiltonian includes nonlinear spin-orbit couplings. Moreover, if the degree of the full Hamiltonian $\geq3$, then the particle current must also be modified in order to satisfy the local conservation law of number.

cond-mat.mes-hall↗

arXiv2007

Some exact identities connecting one- and two-particle Green's functions in spin-orbit coupling systems

Some exact identities connecting the one- and two-particle Green's functions in the presence of spin-orbit coupling have been derived. These identities is similar to the usual Ward identity in the particle or charge transport theory and a satisfying spin transport theory in spin-orbit coupling system should also preserve these identities.

cond-mat.mes-hall↗