Electron transport through a mesoscopic hybrid multiterminal resonant-tunneling system

For a mesoscopic hybrid system which contains a normal central region coupled to multiple superconducting leads, a general expression of the current is derived by using nonequilibrium-Green-function method. This current formula can be used to describe the case with time-dependent external fields applied to any parts of the system, arbitrarily finite voltages, and any kinds of interactions in the central region. For a normal two-terminal interacting electron system, this expression reduces to the general time-dependent current formula previously obtained by Wingreen et al. [Phys. Rev. B 98, 8487 (1993)]. As an application, we use this current formula to study a special case of a noninteracting single-level central region coupled to two or three superconducting leads, respectively.published_or_final_versio

Lack of quenching for the resonant transmission through an inhomogeneously oscillating quantum well

The spectral weights of the wave-function sidebands for a quantum well in the presence of an inhomogeneous electromagnetic (EM) field are studied by introducing a wave function with the form of a Floquet state and then solving the time-dependent Schrödinger equation approximately. The two cases of radiation direction of the EM field parallel and perpendicular to the well axis are considered. We find that the inhomogeneity of the EM field may eliminate the sideband quenching. Based on the spectral weight, the transmission probability through the well is investigated. The energy-level splitting for a special case, the averaged vector potential equal to zero, is also studied.published_or_final_versio

Effect of magnetic field on electron transport in HgTe/CdTe quantum wells: numerical analysis

The effect of magnetic field on electron transport in the inverted band structure of HgTe/CdTe quantum well is investigated. Although magnetic field breaks the time-reversal symmetry, the quantum spin Hall effect can still survive at large magnetic field up to 10 T. Moreover, two quantum anomalous Hall-like phases emerge, in which the system only has a spin-up or spin-down edge state at a given sample edge and the edge current is spin polarized. By tuning the Fermi energy, the system can transit between the quantum spin Hall phase and two quantum anomalous Hall-like phases, so the polarized direction of the edge current is well controllable. Thus the spin selectivity can be realized for potential applications of spintronics. Due to the quantum spin and anomalous Hall-like effects, the longitudinal and Hall resistances exhibit quantum plateaus. In addition, at certain magnetic field, some exotic plateaus like 23 fractional quantum Hall effect are also observed, where edge states with the same spin counterpropagate at the one edge. At last, these plateaus are hardly affected by Rashba spin-orbit interaction, Zeeman effect, and Anderson disorder. © 2012 American Physical Society.published_or_final_versio

Theory of excess noise of a quantum dot in the presence of a microwave field

The power spectrum of excess noise of a quantum dot coupled to two leads and irradiated by a microwave field of frequency Ω is derived exactly by directly solving the Heisenberg equation. We found that for Γ<ħΩ, where Γ is the linewidth of the intradot energy level, the power spectrum can be nonzero even if the averaged current is zero. This property originates from photon-assisted tunneling and is very different from the shot noise in steady state. For Γ≫ħΩ, our results are consistent with the recent experiment by Schoelkopf et al. and previous theory.published_or_final_versio

Spin-polarized transport through a quantum dot: Anderson model with on-site Coulomb repulsion

We report on a theoretical analysis of transport characteristics of a spin-valve system formed by a quantum dot connecting to two ferromagnetic electrodes whose magnetic moments are oriented at an angle θ with respect to each other. We pay special attention to the effects of a finite on-site Coulomb repulsion U. Using the Keldysh nonequilibrium Green’s functions we derived a formula for the current in general terms of bias, temperature, and the parameters θ,U. We have studied the local density of states and nonlinear conductance of this device in the Kondo regime at different polarization angle θ. Our results suggest that the Kondo peaks in the local density of states and in the conductance can be modulated by θ.published_or_final_versio

Interaction between karst terrain and bauxites : evidence from Quaternary orebody distribution in Guangxi, SW China.

Research Article. Geology. 2017.Abstract available in PDF file