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A general theoretical formulation for the effect of a strong on-site Coulomb interaction on the time-dependent electron transport through a quantum dot under the influence of arbitrary time-varying bias voltages and/or external fields is presented, based on slave bosons and the Keldysh nonequilibrium Green's function (GF) techniques. To avoid the difficulties of computing double-time GFs, we generalize the propagation scheme recently developed by Croy and Saalmann to combine the auxiliary-mode expansion with the celebrated Lacroix's decoupling approximation in dealing with the second-order correlated GFs and then establish a closed set of coupled equations of motion, called second-order quantum rate equations (SOQREs), for an exact description of transient dynamics of electron correlated tunneling. We verify that the stationary solution of our SOQREs is able to correctly describe the Kondo effect on a qualitative level. Moreover, a comparison with other methods, such as the second-order von Neumann approach and Hubbard-I approximation, is performed. As illustrations, we investigate the transient current behaviors in response to a step voltage pulse and a harmonic driving voltage, and linear admittance as well, in the cotunneling regime.

The stability of free-standing silicene in oxygen is worthwhile discussing. In this letter, the oxygen adsorption and dissociation on free-standing silicene is studied using first principles. It is found that free-standing silicene is not stable in oxygen because O2 molecules can be easily adsorbed and dissociated into O atoms on a silicene surface without overcoming any energy barrier. Moreover, dissociated oxygen atoms are difficult to migrate on and desorb from silicene surfaces, leading to the formation of Si-O compounds. To enhance the stability of free-standing silicene in oxygen, fully hydrogenated silicene is used as a stabiliser. Interestingly, compared with no energy barrier on pristine silicene, there are two minor energy barriers of O2 molecule adsorption and dissociation on fully hydrogenated silicene, indicating that hydrogenated silicene has higher stability than free-standing silicene in oxygen. However, once the O2 molecule dissociates into two O atoms on hydrogenated silicene, desorption of O atoms will be very difficult due to its high energy barrier. This work will be helpful to understand the detail of O2 molecule dissociation and dissociation-induced O atoms adsorption on free-standing and hydrogenated silicene in oxygen and will be useful to the application of silicene.

We study dc-current effects on the magnetoresistance oscillation in a two-dimensional electron gas with Rashba spin-orbit coupling, using the balance-equation approach to nonlinear magnetotransport. In the weak current limit the magnetoresistance exhibits periodical Shubnikov-de Haas oscillation with changing Rashba coupling strength for a fixed magnetic field. At finite dc bias, the period of the oscillation halves when the interbranch contribution to resistivity dominates. With further increasing current density, the oscillatory resistivity exhibits phase inversion, i.e., magnetoresistivity minima (maxima) invert to maxima (minima) at certain values of the dc bias, which is due to the current-induced magnetoresistance oscillation.

Considering electron-impurity and electron-phonon scattering, we present a balance-equation-based theoretical examination of thermoelectric power (TEP) in a two-dimensional single-layer graphene away from the carrier neutrality point. Both the boundary scattering and phonon-phonon interaction in phonon relaxation processes are taken into account. We find that, at temperatures T > 10 K, the contribution to TEP mainly comes from diffusive processes and the phonon-drag effect can be ignored. However, at T ≤ 10 K, the phonon-phonon interaction leads to a phonon-drag peak in the temperature dependence of TEP. We also compare our results with experiments.

Using a nonequilibrium Green function approach, we systematically investigate the current induced spin polarization (CISP) in a two-dimensional heavy-hole system with cubic Rashba spin-orbit coupling, driven by in-plane electric and magnetic fields. We find that when a magnetic field is applied along the direction of electric field, the longitudinal conductivity drops monotonously with an increase of magnetic-field strength or of hole density. The spin polarization along the electric-field direction is just the Pauli paramagnetism and it quadratically increases with an increase of hole density. The nonvanishing out-of-plane component of spin polarization emerges for both short-range and long-range disorders, and it changes sign with the variation of magnetic field, especially for long-range hole-impurity scattering. In the magnetic-field dependences of this out-of-plane CISP and of the in-plane CISP perpendicular to the electric field, there are singular magnetic fields, below or above which the effects of magnetic field are completely different., (© 2010 IOP Publishing Ltd)

Considering electron-impurity, electron-acoustic-phonon and electron-optical-phonon scatterings, the nonlinear steady-state transport properties of graphene are studied theoretically by means of the balance equation approach. We find that the conductivity as a function of electric field strength, E, exhibits strongly nonlinear behavior for E larger than a critical value, E(c)≈0.1 kV cm(-1). With the increase of E from zero, the conductivity first decreases slowly and then it falls rapidly when E>E(c). The dependence of electron temperature on E is also demonstrated.