arXiv subjects

Zhongshui Ma

Publications and source records attributed to Zhongshui Ma.

26 records · Page 2Linked to original sources

arXiv2007

Orientation dependence of the optical spectra in graphene at high frequencies

On the basis of the Kubo formula we evaluated the optical conductivity of a graphene sheet. The full behavior of frequency as well as temperature dependence of the optical conductivity is presented. We show that the anisotropy of conductivity can be significantly enhanced at high frequencies. The photon absorption depends on the field polarization direction. At the frequency comparable to the maximum separation of upper and lower bands the photon-induced conduction of electrons is strongly suppressed if the polarization of field is along the zigzag direction. The corresponding optical conductivity is several orders of magnitude weaker than that when the light is polarizing along the armchair direction. We propose that the property of orientation selection of absorption in the graphene can be used as a basis for a high-frequency partial polarizer.

cond-mat.mes-hall↗

arXiv2007

Enhancement of polarization in a spin-orbit coupling quantum wire with a constriction

We investigate the enhancement of spin polarization in a quantum wire in the presence of a constriction and a spin-orbit coupling segment. It is shown that the spin-filtering effect is significantly heightened in comparison with the configuration without the constriction. It is understood in the studies that the constriction structure plays a critical role in enhancing the spin filtering by means of confining the incident electrons to occupy one channel only while the outgoing electrons occupy two channels. The enhancement of spin-filtering has also been analyzed within the perturbation theory. Because the spin polarization arises mainly from the scattering between the constriction and the segment with spin-orbit coupling, the sub-band mixing induced by spin-orbit interaction in the scattering process and the interferences result in higher spin-filtering effect.

cond-mat.mes-hall↗

arXiv2007

Time reversal Aharonov-Casher effect in mesoscopic rings with Rashba spin-orbital interaction

The time reversal Aharonov-Casher (AC) interference effect in the mesoscopic ring structures, based on the experiment in Phys. Rev. Lett. \textbf{97}, 196803 (2006), is studied theoretically. The transmission curves are calculated from the scattering matrix formalism, and the time reversal AC interference frequency is singled out from the Fourier spectra in numerical simulations. This frequency is in good agreement with analytical result. It is also shown that in the absent of magnetic field, the Altshuler-Aronov-Spivak type (time reversal) AC interference retains under the influence of strong disorder, while the Aharonov-Bohm type AC interference is suppressed.

cond-mat.mes-hall↗

arXiv2005

Consistency in Formulation of Spin Current and Torque Associated with a Variance of Angular Momentum

Stimulated generally by recent interest in the novel spin Hall effect, the nonrelativistic quantum mechanical conserved currents, taken into account of spin-orbit coupling, are rigorously formulated based on the symmetries of system and Noether' theorem. The quantum mechanical force on the spin as well as the torque associated with the variance of angular momentum are obtained. Consequently, the kinetic interpretation of the variances of spin and orbit angular momentum currents implies a torque on the "electric dipole" associated with the moving spin. The bearing of the force and the torque on the properties of spin current in a two-dimensional electron gas with the Rashba spin-orbit interaction is discussed.

cond-mat.mes-hall↗

arXiv2004

Controllable quantum spin precession by Aharonov-Casher phase in conducting ring

We investigate quantum spin transport in a structure of conducting ring, embedded in textured electric field, with two leads, and obtain an exact solution for the problem. The spin precession induced by the Aharonov-Casher phase is studied. It is shown that the spin-polarized current and its polarizability can be controlled by the electric field. As a result the polarizability is a function of the geometric phase which originates from the spin-orbital interaction in the ring. 72.25.-b, 03.65.Vf

cond-mat.mes-hall↗

arXiv2003

Quantum measurement of a solid-state qubit: A unified quantum master equation approach revisited

Quantum measurement of a solid-state qubit by a mesoscopic detector is of fundamental interest in quantum physics and an essential issue in quantum computing. In this work, by employing a unified quantum master equation approach constructed in our recent publications, we study the measurement-induced relaxation and dephasing of the coupled-quantum-dot states measured by a quantum-point-contact. Our treatment pays particular attention on the detailed-balance relation, which is a consequence of properly accounting for the energy exchange between the qubit and detector during the measurement process. As a result, our theory is applicable to measurement at arbitrary voltage and temperature. Both numerical and analytical results for the qubit relaxation and dephasing are carried out, and new features are highlighted in concern with their possible relevance to future experiments.

cond-mat.mes-hall↗

arXiv2003

Photon-assisted Fano Resonance and Corresponding Shot-Noise in a Quantum Dot

We have studied the Fano resonance in photon-assisted transport in a quantum dot and calculated both the coherent current and spectral density of shot noise. It is predicted, for the first time, that the shape of Fano profile will also appear in satellite peaks. It is found that the variations of Fano profiles with the strengths of nonresonant transmissions are not synchronous in absorption and emission sidebands. The effect of interference on photon-assisted pumped current has been also investigated. We further predict the current and spectral density of shot noise as a function of the phase, which exhibits an intrinsic property of resonant and nonresonant channels in the structures.

cond-mat.mes-hall↗

arXiv2001

Dephasing Effect in Photon-Assisted Resonant Tunneling through Quantum Dots

We analyze dephasing in single and double quantum dot systems. The decoherence is introduced by the Büttiker model with current conserving fictitious voltage leads connected to the dots. By using the non-equilibrium Green function method, we investigate the dephasing effect on the tunneling current. It is shown that a finite dephasing rate leads to observable effects. The result can be used to measure dephasing rates in quantum dots.

cond-mat.mes-hall↗