arXiv subjects

Xiao-Bing Wang

Publications and source records attributed to Xiao-Bing Wang.

3 recordsLinked to original sources

arXiv2002

Dephasing time of disordered two-dimensional electron gas in modulated magnetic fields

The dephasing time of disordered two-dimensional electron gas in a modulated magnetic field is studied. It is shown that in the weak inhomogeneity limit, the dephasing rate is proportional to the field amplitude, while in strong inhomogeneity limit the dependence is quadratic. It is demonstrated that the origin of the dependence of dephasing time on field amplitude lies in the nature of corresponding single-particle motion. A semiclassical Monte Carlo algorithm is developed to study the dephasing time, which is of qualitative nature but efficient in uncovering the dependence of dephasing time on field amplitude for arbitrarily complicated magnetic-field modulation. Computer simulations support analytical results. The crossover from linear to quadratic dependence is then generalized to the situation with magnetic field modulated periodically in one direction with zero mean, and it is argued that this crossover can be expected for a large class of modulated magnetic fields.

cond-mat.mes-hall↗

arXiv2001

Conductance fluctuations in a quantum dot under almost periodic ac pumping

It is shown that the variance of the linear dc conductance fluctuations in an open quantum dot under a high-frequency ac pumping depends significantly on the spectral content of the ac field. For a sufficiently strong ac field $γτ_ϕ<< 1$, where $1/τ_ϕ$ is the dephasing rate induced by ac noise and $γ$ is the electron escape rate, the dc conductance fluctuations are much stronger for the harmonic pumping than in the case of the noise ac field of the same intensity. The reduction factor $r$ in a static magnetic field takes the universal value of 2 only for the white--noise pumping. For the strictly harmonic pumping $A(t)=A_{0}\cosωt$ of sufficiently large intensity the variance is almost insensitive to the static magnetic field $r-1= 2\sqrt{τ_ϕγ} << 1$. For the quasi-periodic ac field of the form $A(t)=A_{0} [\cos(ω_{1} t)+\cos(ω_{2} t)]$ with $ω_{1,2} >> γ$ and $γτ_ϕ << 1$ we predict the novel effect of enchancement of conductance fluctuations at commensurate frequencies $ω_{2}/ω_{1}=P/Q$.

cond-mat.mes-hall↗

arXiv1998

Ward Identities for Interacting Electronic Systems

A Ward-Takahashi identity, as a consequence of gauge invariance and in a form that relates self-energy to the two-particle Bethe-Salpeter scattering kernel, was first derived by Vollhardt and Wölfle for a system of independent particles moving in a random medium. This is generalized to a class of interacting electronic systems in materials with or without random impurities, following a procedure previously used for classical waves transport in disordered media. This class of systems also possesses other symmetry properties such as invariance under time translations and local spin rotations, which imply local conservation laws for energy and spin current. They imply additional Vollhardt-Wölfle type identities. We present non-perturbative derivations of these identities, and consider the constraints they impose on the relationship between the self-energy and the two-particle scattering kernel.

cond-mat↗