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In this paper, we investigate the electronic transport properties of a quantum dot (QD) connected to two ferromagnetic leads and one superconductor lead in the Kondo regime by means of the finite-$U$ slave boson mean field approach and nonequilibrium Green function technique. In this three-terminal hybrid nano-device, we will focus our attention on the joint effects of the Konod correlation, superconducting proximity pairing, and spin polarization of leads. It is found that: the superconducting proximity effect will suppress the linear local conductance (LLC) stemming from the weakened Kondo peak, and when its coupling $\Gamma_s$ is bigger than the tunnel-coupling $\Gamma$ of two normal leads, the linear cross conductance (LCC) becomes negative in the Kondo region; for antiparallel configuration, increasing spin polarization further suppresses LLC but enhances LCC, i.e. causing larger negative values of LCC, since it is benefit for emergence of cross Andreev reflection; On the contrary, for parallel configuration, with increasing spin polarization, the LLC descends and greatly widens with the appearance of shoulders, and eventually splits into four peaks, and meanwhile the LCC reduces relatively rapidly to the normal conductance., Comment: 9 pages, 6 figures

We investigate the transport properties through a finite dimer chain connected to two normal leads or one normal and one superconductor (SC) leads. The dimer chain is described by the Su-Schrieffer-Hegger model and can be tuned into a topologically nontrivial phase with a pair of zero-energy edge states (ZEESs). We find that if the dimer chain is of nontrivial topology, (1) it will show apparent but opposite odd-even parity of the number of sites, in comparison with the topologically trivial and plain chains, in the (Andreev) transmission probability at the Fermi energy (i.e. the conductance and the Andreev conductance), the noise Fano factor in the zero bias limit, and even the transmission phase due to the coupled ZEESs; (2) the ZEES can determine appearance of the Andreev bound states at the site connected to the SC lead, and thereby induces a nonzero-bias-anomaly in the Andreev differential conductance of the hybrid junction; (3) the transmission phase of the normal junction has a unique $2\pi$ continuous phase variation at the zero-energy resonant peak that is also different from the usual phase shift in resonant point in usual systems., Comment: 6 pages, 6 figures

We present a theoretical investigation for the full counting statistics of the Andreev tunneling through a quantum dot (QD) embedded between superconducting (SC) and normal leads in the presence of a strong on-site electron-phonon interaction using nonequilibrium Green function method. For this purpose, we generalize the dressed tunneling approximation (DTA) recently developed in dealing with inelastic tunneling in a normal QD system to the Andreev transport issue, which takes account of vibrational effect in evaluation of electronic tunneling self energy in comparison with other simple approaches and meanwhile allows us to derive an explicit analytical formula for the cumulant generating function at the subgap region. We then analyze the interplay of polaronic and SC proximity effects on the Andreev reflection spectrum, current-voltage characteristics, and current fluctuations of the hybrid system. Our main findings include: (1) no phonon side peaks in the linear Andreev conductance; (2) a negative differential conductance stemming from the suppressed Andreev reflection spectrum; (3) a novel inelastic resonant peak in the differential conductance due to phonon assisted Andreev reflection; (4) enhancement or suppression of shot noise for the symmetric or asymmetric tunnel-coupling system respectively., Comment: 15 pages, 13 figures,submitted

Considering the interband correlation, we present a generalized multiple-scattering approach of Green's function to investigate the effects of electron-impurity scattering on the density of states in silicene. The reduction of energy gaps in the case of relatively high chemical potential and the transformation of split-off impurity bands into band tails for low chemical potential are found. The dependency of optical conductivity on the impurity concentration is also discussed for frequency within the terahertz regime., Comment: 10 pages, 8 figures, submitted to PRB

A momentum balance equation is developed to investigate the magnetotransport properties in monolayer molybdenum disulphide when a strong perpendicular magnetic field and a weak in-plane electric field are applied simultaneously. At low temperature, in the presence of intravalley impurity scattering Shubnikov de Haas oscillation shows up accompanying by a beating pattern arising from large spin splitting and its period may halve due to high-order oscillating term at large magnetic field for samples with ultrahigh mobility. In the case of intervalley disorders, there exists a magnetic-field range where the magnetoresistivity almost vanishes. For low-mobility layer, a phase-inversion of oscillating peaks is acquired in accordance with recent experiment. At high temperature when Shubnikov de Haas oscillation is suppressed, the magnetophonon resonances induced by both optical phonons (mainly due to homopolar and Fr\"ohlich modes) and acoustic phonons (mainly due to intravalley transverse and longitudinal acoustic modes) emerge for suspended system with high mobility. For the single layer on a substrate, another resonance due to surface optical phonons may occur, resulting in a complex behavior of the total magnetoresistance. The beating pattern of magnetophonon resonance due to optical phonons can also be observed. However, for nonsuspended layer with low mobility, the magnetoresistance oscillation almost disappears and the resistivity increases with field monotonously.

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 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., Comment: 16 pages, 9 figures

Considering finite-temperature screened electron-impurity scattering, we present a kinetic equation approach to investigate transport properties of two-dimensional massive fermions in silicene. We find that the longitudinal conductivity is always nonvanishing when chemical potential lies within the energy gap. This residual conductivity arises from interband correlation and strongly depends on strength of electron-impurity scattering. We also clarify that the electron-impurity interaction makes substantial contributions to the spin- and valley-Hall conductivities, which, however, are almost independent of impurity density. The dependencies of longitudinal conductivity as well as of spin- and valley-Hall conductivities on chemical potential, on temperature, and on gap energy are analyzed., Comment: Minor correction, accepted for publication in PRB

The oxygen adsorption and dissociation on pristine silicene surface are studied by use of first-principles in this letter. The oxygen adsorption and dissociation on pristine silicene surface are studied by use of first-principles in this letter. It is found that the pristine silicene is not stable in air because the oxygen molecule can be easily adsorbed and dissociated into two O atoms without overcoming any energy barrier on pristine silicene surface. In addition, dissociated oxygen atoms are relatively difficult to migrate on or desorbed from pristine silicene surface, leading to poor mobility of oxygen atom. As a result, silicene would be changed into Si-O compounds in air. The work will be helpful to reveal the detail of the interaction between oxygen molecules and pristine silicene surface, especially helpful to understand the stability of silicene in air.

We investigate the full counting statistics of a single quantum dot strongly coupled to a local phonon and weakly tunnel-connected to two metallic electrodes. By employing the generalized nonequilibrium Green function method and the Lang-Firsov transformation, we derive an explicit analytical formula for the cumulant generating function, which makes one to be able to identify distinctly the elastic and inelastic contributions to the current and zero-frequency shot noise. We find that at zero temperature, the inelastic effect causes upward steps in the current and downward jumps in the noise at the bias voltages corresponding to the opening of the inelastic channels, which are ascribed to the vibration-induced complex dependences of electronic self-energies on the energy and bias voltage. More interestingly, the Fano factor exhibits oscillatory behavior with increasing bias voltage and its minimum value is observed to be smaller than one half., Comment: 12 pages, 6 figures

A balance-equation scheme is developed to investigate the magnetotransport in a dc-current-biased graphene. We examine the Shubnikov-de Haas oscillation under a nonzero bias current. With an increase in the current density, the oscillatory differential resistivity exhibits phase inversion, in agreement with recent experimental observation. In the presence of surface optical phonons, a second phase inversion may occur at higher dc bias, due to the reduced influence of electron-heating and the enhanced direct effect of current on differential magnetoresistivity. We also predict the appearance of current-induced magnetoresistance oscillation in suspended graphene at lower magnetic fields and larger current densities. For the graphene mobility currently available ($\approx 20\,{\rm m^2/Vs}$), the oscillatory behavior may be somewhat altered by magnetophonon resonance arising from intrinsic acoustic phonon under finite bias current condition., Comment: 10 pages, 6 figures, accepted for publication in Phys. Rev. B

We examine the effect of changing the linear polarization angle $\theta$ of incident microwaves with respect to the dc current on radiation-induced magnetoresistance oscillations in a two-dimensional (2D) system within the balance-equation formulation of the photon-assisted magnetotransport model, considering the radiative decay as the sole damping mechanism. At an extremum the amplitude of oscillatory magnetoresistance $R_{xx}$ exhibits a sinusoidal, up to a factor of 5, magnitude variation with rotating the polarization angle $\theta$. The maximal amplitude shows up generally at a nonzero $\theta$, which is dependent upon the extremum in question, the 2D electron setup, the radiation frequency and the magnetic field orientation. These results provide a natural explanation for the experimental observations by Mani {\it et al.} [Phys. Rev. B {\bf 84}, 085308 (2011)], and Ramanayaka {\it et al.} [Phys. Rev. B {\bf 85}, 205315 (2012)]., Comment: 5 pages, two figures

A positive, non-saturating and dominantly linear magnetoresistance is demonstrated to occur in the surface state of a topological insulator having a wavevector-linear energy dispersion together with a finite positive Zeeman energy splitting. This linear magnetoresistance shows up within quite wide magnetic-field range in a spatially homogenous system of high carrier density and low mobility in which the conduction electrons are in extended states and spread over many smeared Landau levels, and is robust against increasing temperature, in agreement with recent experimental findings in Bi$_2$Se$_3$ nanoribbons., Comment: 7 pages, 4 figures

We study the full counting statistics (FCS) of electron tunneling through a multi-terminal quantum dot in the Kondo regime within the slave-boson mean field theory. By employing the A.O. Gogolin and A. Komnik's method of calculating the FCS generating function based on the nonequilibrium Green's function [Phys. Rev. B {\bf 73}, 195301 (2006)], we obtain the counting field $\lambda$-dependent self-consistent equations for the mean values of the slave-boson fields and the explicit expression for the derivative of the adiabatic potential of the system with respect to the counting fields. Performing perturbative expansion to the first order of $\lambda$, we find an extra contribution to the shot noise due to the bias-induced Bose field fluctuation, and then confirm that the nonequilibrium particle number fluctuation plays an important role in the current noise of the Kondo dot: enhancement of the current auto-correlation and a positive current cross-correlation., Comment: 11 pages, 3 figures, to be published

Considering screeening of electron scattering interactions in terms of the finite-temperature STLS theory and solving the linearized Boltzmann equation (with no appeal to a relaxation time approximation), we present a theoretical analysis of the low-temperature Seebeck effect in two-dimensional semiconductors with dilute electron densities. We find that the temperature ($T$) dependencies of the diffusion and phonon-drag thermoelectric powers ($S_d$ and $S_g$) can no longer be described by the conventional simple power-laws. As temperature increases, $|S_d|/T$ decreases when $T\gtrsim 0.1 \epsilon_F$ ($\epsilon_F$ is the Fermi energy), while $|S_g|$ first increases and then falls, resulting a peak located at a temperature between Bloch-Gr\"uneisen temperature and $\epsilon_F$., Comment: 12 pages, 5 figures

We examine cross-correlations (CCs) in the tunneling currents through two parallel interacting quantum dots coupled to four independent ferromagnetic electrodes. We find that when either one of the two circuits is in the parallel configuration with sufficiently strong polarization strength, a new mechanism of dynamical spin blockade, i.e., a spin-dependent bunching of tunneling events, governs transport through the system together with the inter-dot Coulomb interaction, leading to a sign-reversal of the zero-frequency current CC in the dynamical channel blockade regime, and to enhancement of positive current CC in the dynamical channel anti-blockade regimes, in contrast to the corresponding results for the case of paramagnetic leads., Comment: 9 pages, 3 figures

We examine the current-induced magnetoresistance oscillations in high-mobility two-dimensional electron systems using the balance-equation scheme for nonlinear magnetotransort. The reported analytical expressions for differential magnetoresistivity at high filling factors in the overlapping Landau-level regime, which show good agreement with the experimental observation and the numerical calculation, may be helpful in extracting physical information from experiments., Comment: 4 pages, 2 figures

We analyze the effects of a distortion of the nuclear potential of a molecular quantum dot (QD), as well as a shift of its equilibrium position, on nonequilibrium-vibration-assisted tunneling through the QD with a single level ($\epsilon_d$) coupled to the vibrational mode. For this purpose, we derive an explicit analytical expression for the Franck-Condon (FC) factor for a displaced-distorted oscillator surface of the molecule and establish rate equations in the joint electron-phonon representation to examine the current-voltage characteristics and zero-frequency shot noise, and skewness as well. Our numerical analyses shows that the distortion has two important effects. The first one is that it breaks the symmetry between the excitation spectra of the charge states, leading to asymmetric tunneling properties with respect to $\epsilon_d>0$ and $\epsilon_d<0$. Secondly, distortion (frequency change of the oscillator) significantly changes the voltage-activated cascaded transition mechanism, and consequently gives rise to a different nonequilibrium vibrational distribution from that of the case without distortion. Taken in conjunction with strongly modified FC factors due to distortion, this results in some new transport features: the appearance of strong NDC even for a single-level QD with symmetric tunnel couplings; a giant Fano factor even for a molecule with an extremely weak electron-phonon interaction; and enhanced skewness that can have a large negative value under certain conditions., Comment: 29 pages, 11 figures, published version

Microwave-induced nonlinear magnetoresistance in a dc-driven two-dimensional electron system is examined using a multi-photon-assisted transport scheme direct controlled by the current. It is shown that near the 2nd subharmonic of the cyclotron resonance, the frequency of the resistivity oscillation with the magnetic-field-normalized current-density is double that at the cyclotron resonance and its harmonics, in excellent agreement with recent experimental findings by Hatke {\it et al.} [Phys. Rev. Lett. {\bf 101}, 246811 (2008)]. The current-induced alternative emergence of resonant two-photon and single-photon processes is responsible for this frequency doubling. Near the third subharmonic of the cyclotron resonance, the current-induced consecutive appearance of resonant 0-/3-photon, two-photon, and single-photon processes may lead to the frequency tripling of the resistivity oscillation., Comment: 6 pages, 2 figures, published version

Nonlinear magnetotransport of a microwave-irradiated high mobility two-dimensional electron system under a finite direct current excitation is analyzed using a dc-controlled scheme with photon-assisted transition mechanism. The predicted amplitudes, extrema and nodes of the oscillatory differential resistance versus the magnetic field and the current density, are in excellent agreement with the recent experimental observation [Hatke et al. Phys. Rev. B 77, 201304(R) (2008)]., Comment: 4 pages, 2 figures

We examine the shot noise spectrum properties of coherent resonant tunneling in coupled quantum dots in both series and parallel arrangements by means of quantum rate equations and MacDonald's formula. Our results show that, for a series-CQD with a relatively high dot-dot hopping $\Omega$, $\Omega/\Gamma\gtrsim 1$ ($\Gamma$ denotes the dot-lead tunnel-coupling strength), the noise spectrum exhibits a dip at the Rabi frequency, $2\Omega$, in the case of noninteracting electrons, but the dip is supplanted by a peak in the case of strong Coulomb repulsion; furthermore, it becomes a dip again for a completely symmetric parallel-CQD by tuning enclosed magnetic-flux., Comment: 8 pages, 5 figures

We investigate nonlinear thermal transport properties of a single interacting quantum dot with two energy levels tunnel-coupled to two electrodes using nonequilibrium Green function method and Hartree-Fock decoupling approximation. In the case of asymmetric tunnel-couplings to two electrodes, for example, when the upper level of the quantum dot is open for transport, whereas the lower level is blocked, our calculations predict a strong asymmetry for the heat (energy) current, which shows that, the quantum dot system may act as a thermal rectifier in this specific situation., Comment: 5 pages, 5 figures

In this paper, we analyze vibration-assisted sequential tunneling (including current-voltage characteristics and zero-frequency shot noise) through a molecular quantum dot with two electronic orbitals asymmetrically coupled to the internal vibration. We employ rate equations for the case of equilibrated phonons, and strong Coulomb blockade. We find that a system with a strongly phonon-coupled ground state orbital and weakly phonon-coupled excited state orbital exhibits strong negative differential conductance; and it also shows super-Poissonian current noise. We discuss in detail the reasons and conditions for the appearance of negative differential conductance., Comment: 6 pages, 6 figures, and 1 table

Effects of resonant acoustic phonon scattering on magnetoresistivity are examined in two-dimensional electron systems at low temperatures by using a balance-equation magnetotransport scheme direct controlled by the current. The experimentally observed resonances in linear resistivity are shown to result from the conventional bulk phonon modes in a GaAs-based system, without invoking leaky interface phonons. Due to quick heating of electrons, phonon resonances can be dramatically enhanced by a finite bias current. When the electron drift velocity increases to the speed of sound, additional and prominent phonon resonance peaks begin to emerge. As a result, remarkable resistance oscillation and negative differential resistivity can appear in nonlinear transport in a modest mobility sample at low temperatures, which is in agreement with recent experiments., Comment: 7 pages, 5 figures, published version

We carry out a detailed analysis of coherent resonant tunneling through two coupled quantum dots (CQD) in a parallel arrangement in the weak tunneling limit. We establish a set of quantum rate equations (QREs) in terms of the eigenstate-representation by means of a generic quantum Langevin equation approach, which is valid for arbitrary bias-voltage, temperature, and interdot hopping strength. Based on linear-response theory, we further derive the current and frequency-independent shot noise formulae. Our results reveal that a previously used formula for evaluating Schottky-type noise of a "classical" single-electron transistor is a direct result of linear-response theory, and it remains applicable for small quantum devices with internal coupling. Our numerical calculations show some interesting transport features (i) for a series-CQD: the appearance of a NDC due to the bias-voltage-induced shifting of bare levels or a finite interdot Coulomb repulsion, and (ii) for a parallel CQD in strong interdot Coulomb repulsion regime: finite-bias-induced AB oscillations of current, and magnetic-flux-controllable negative differential conductance and a huge Fano factor., Comment: 14 pages, 12 figures

We study the effect of electron-phonon interaction on current and zero-frequency shot noise in resonant tunneling through a series triple-quantum-dot coupling to a local phonon mode by means of a nonperturbative mapping technique along with the Green function formulation. By fixing the energy difference between the first two quantum dots to be equal to phonon frequency and sweeping the level of the third quantum dot, we find a largely enhanced current spectrum due to phonon effect, and in particular we predict current peaks corresponding to phonon-absorption and -emission assisted resonant tunneling processes, which shows that this system can be acted as a sensitive phonon-signal detector or as a cascade phonon generator., Comment: 3 pages, 3 figures

We analyze inelastic cotunneling through an interacting quantum dot subject to an ambient magnetic field in the weak tunneling regime under a non-adiabatic time-dependent bias-voltage. Our results clearly exhibit photon-assisted satellites and an overall suppression of differential conductance with increasing driving amplitude, which is consistent with experiments. We also predict a zero-anomaly in differential conductance under an appropriate driving frequency., Comment: Phys. Lett. A (in press)

We present a kinetic equation approach to investigate dc transport properties of graphene in the diffusive regime considering long-range electron-impurity scattering. In our study, the effects of interband correlation (or polarization) on conductivity are taken into account. We find that the conductivity contains not only the usual term inversely proportional to impurity density $N_i$, but also an anomalous term that is linear in $N_i$. This leads to a minimum in the density dependence of conductivity when the electron density $N_{\rm e}$ is equal to a critical value, $N_c$. For $N_{\rm e}>N_c$ the conductivity varies almost linearly with the electron density, while it is approximately inversely proportional to $N_{\rm e}$ when $N_{\rm e}

Magnetoresistance oscillations in two-dimensional electron systems driven simultaneously by a strong direct current and a microwave irradiation, are analyzed within a unified microscopic scheme treating both excitations on an equal footing. The microwave-induced resistance oscillations are described by a parameter $\epsilon_\omega$ proportional to the radiation frequency, while the dc-induced resistance oscillations are governed by a parameter $\epsilon_j$ proportional to the current density. In the presence of both a microwave radiation and a strong dc, the combined parameter $\epsilon_\omega+\epsilon_j$ is shown to control the main resistance oscillations, in agreement with the recent measurement [Zhang {\it et al.} Phys. Rev. Lett. {\bf 98}, 106804 (2007)], Comment: 4 pages, 2 figues, published version

Motivated by a recent experiment on nonlinear tunneling in a suspended Carbon nanotube connected to two normal electrodes [S. Sapmaz, {\it et al}., Phys. Rev. Lett. {\bf 96}, 26801 (2006)], we investigate nonequilibrium vibration-mediated sequential tunneling through a molecular quantum dot with two electronic orbitals asymmetrically coupled to two electrodes and strongly interacting with an internal vibrational mode, which is itself weakly coupled to a dissipative phonon bath. For this purpose, we establish rate equations using a generic quantum Langevin equation approach. Based on these equations, we study in detail the current-voltage characteristics and zero-frequency shot noise, paying special attention to the advanced or postponed of the appearance of negative differential conductance and super-Poissonian current noise resulting from electron-phonon-coupling induced {\em selective unidirectional cascades of single-electron transitions}., Comment: 11 pages, 7 figures

We analyze resonant tunneling subject to a non-adiabatic time-dependent bias-voltage through an asymmetric single molecular quantum dot with coupling between the electronic and vibrational degrees of freedom using a {\em Tien-Gordon-type} rate equation. Our results clearly exhibit the appearance of photon-assisted satellites in the current-voltage characteristics and the elimination of hot-phonon-induced negative differential conductance with increasing ac driving amplitude for an asymmetric system. This can be ascribed to an {\em ac-induced suppression} of unequilibrated (hot) phonons in an asymmetric system., Comment: Accepted by Appl. Phys. Lett

We study inelastic cotunneling through a strong Coulomb-blockaded quantum dot subject to a static magnetic field and a perpendicular circularly-polarized magnetic field using a quantum Langevin equation approach. Our calculation predicts an interesting controllable cotunneling current characteristic, splitting--zero-anomaly--splitting transition of the differential conductance with increasing the driving frequency, ascribing to the role of {\em photon-assisted spin-flip} cotunneling processes., Comment: 5 pages, 3 figures, published version in Phys. Rev. B

We report our studies of zero-frequency shot noise in tunneling through a parallel-coupled quantum dot interferometer by employing number-resolved quantum rate equations. We show that the combination of quantum interference effect between two pathways and strong Coulomb repulsion could result in a giant Fano factor, which is controllable by tuning the enclosed magnetic flux., Comment: 11 pages, 2 figures

Electric current-induced magnetoresistance oscillations recently discovered in two-dimensional electron systems are analyzed using a microscopic scheme for nonlinear magnetotransport direct controlled by the current. The magnetoresistance oscillations are shown to result from drift-motion assisted electron scatterings between Landau levels. The theoretical predictions not only reproduce all the main features observed in the experiments but also disclose other details of the phenomenon., Comment: 4 pages, 3 figures, published version

We employ a helicity-basis kinetic equation approach to investigate the anomalous Hall effect in two-dimensional narrow-band semiconductors considering both Rashba and extrinsic spin-orbit (SO) couplings, as well as a SO coupling directly induced by an external driving electric field. Taking account of long-range electron-impurity scattering up to the second Born approximation, we find that the various components of the anomalous Hall current fit into two classes: (a) side-jump and (b) skew scattering anomalous Hall currents. The side-jump anomalous Hall current involves contributions not only from the extrinsic SO coupling but also from the SO coupling due to the driving electric field. It also contains a component which arises from the Rashba SO coupling and relates to the off-diagonal elements of the helicity-basis distribution function. The skew scattering anomalous Hall effect arises from the anisotropy of the diagonal elements of the distribution function and it is a result of both the Rashba and extrinsic SO interactions. Further, we perform a numerical calculation to study the anomalous Hall effect in a typical InSb/AlInSb quantum well. The dependencies of the side-jump and skew scattering anomalous Hall conductivities on magnetization and on the Rashba SO coupling constant are examined., Comment: 16 pages, 4 figures, accepted for publication in PRB

The frequency dependence of the peak-valley pairs occurring in the magnetoresistivity of a two-dimensional electron system under enhanced microwave irradiation, which are considered to associate with multiphoton processes, is examined in the sub-cyclotron-frequency range, based on a theoretical treatment with photon-assisted electron transitions due to impurity scattering. It is shown that with equivalent radiation power (producing the same height of the main oscillation peak), much more and stronger multi-photon structures show up at lower frequency, and when frequency increases all these structures rapidly weaken, diminish and finally disappear completely. These are in agreement with the recent experimental observation [cond-mat/0608633]., Comment: 2 pages, 2 figures

The magnetoresistance oscillations in high-mobility two-dimensional electron systems induced by two radiation fields of frequencies 31 GHz and 47 GHz, are analyzed in a wide magnetic-field range down to 100 G, using the balance-equation approach to magnetotransport for high-carrier-density systems. The frequency mixing processes are shown to be important. The predicted peak positions, relative heights, radiation-intensity dependence and their relation with monochromatic resistivities are in good agreement with recent experimental finding [M. A. Zudov {\it et al.} Phys. Rev. Lett. 96, 236804 (2006)]., Comment: 4 pages, 3 figures

Motivated by a recent experiment[Nature {\bf 442}, 176 (2006)], we present a quantitative microscopic theory to investigate the inverse spin-Hall effect with spin injection into aluminum considering both intrinsic and extrinsic spin-orbit couplings using the orthogonalized-plane-wave method. Our theoretical results are in good agreement with the experimental data. It is also clear that the magnitude of the anomalous Hall resistivity is mainly due to contributions from extrinsic skew scattering, while its spatial variation is determined by the intrinsic spin-orbit coupling., Comment: 5 pages, 3 figures

A nonequilibrium Green's function approach is employed to investigate the spin-Hall effect in diffusive two-dimensional electron systems with Rashba spin-orbit interaction. Considering a long-range electron-impurity scattering potential in the self-consistent Born approximation, we find that the spin-Hall effect arises from two distinct interband polarizations in helicity basis: a disorder-unrelated polarization directly induced by the electric field and a polarization mediated by electron-impurity scattering. The disorder-unrelated polarization is associated with all electron states below the Fermi surface and produces the original intrinsic spin-Hall current, while the disorder-mediated polarization emerges with contribution from the electron states near the Fermi surface and gives rise to an additional contribution to the spin-Hall current. Within the diffusive regime, the total spin-Hall conductivity vanishes in {\it infinitely large} samples, independently of temperature, of the spin-orbit coupling constant, of the impurity density, and of the specific form of the electron-impurity scattering potential. However, in a {\it finite-size} Rashba two-dimensional semiconductor, the spin-Hall conductivity no longer always vanishes. Depending on the sample size in the micrometer range, it can be positive, zero or negative with a maximum absolute value reaching as large as $e/8\pi$ order of magnitude at low temperatures. As the sample size increases, the total spin-Hall conductivity oscillates with a decreasing amplitude. We also discuss the temperature dependence of the spin-Hall conductivity for different sample sizes., Comment: 9 pages, 3 figures, extended version of cond-mat/0411629

We analyze the magnetoresistance $R_{xx}$ oscillations in high-mobility two-dimensional electron systems induced by the combined driving of two radiation fields of frequency $\omega_1$ and $\omega_2$, based on the balance-equation approach to magnetotransport for high-carrier-density systems in Faraday geometry. It is shown that under bichromatic irradiation of $\omega_2\sim 1.5 \omega_1$, most of the characterstic peak-valley pairs in the curve of $R_{xx}$ versus magnetic field in the case of monochromatic irradiation of either $\omega_1$ or $\omega_2$ disappear, except the one around $\omega_1/\omega_c\sim 2$ or $\omega_2/\omega_c\sim 3$. $R_{xx}$ oscillations show up mainly as new peak-valley structures around other positions related to multiple photon processes of mixing frequencies $\omega_1+\omega_2$, $\omega_2-\omega_1$, etc. Many minima of these resistance peak-valley pairs can descend down to negative with enhancing radiation strength, indicating the possible bichromaticzero-resistance states., Comment: 5 pages, 3 figures. Accepted for publication in Phys. Rev. B

Recently discovered new structures and zero-resistance states outside the well-known oscillations are demonstrated to arise from multiphoton assisted processes, by a detailed analysis of microwave photoresistance in two-dimensional electron systems under enhanced radiation. The concomitant resistance dropping and peak narrowing observed in the experiments are also reproduced. We show that the radiation-induced suppression of average resistance comes from virtual photon effect and exists throughout the whole magnetic field range., Comment: 4 pages, 2 figures, published version

Employing a nonequilibrium Green's function approach, we examine the effects of long-range hole-impurity scattering on spin-Hall current in $p$-type bulk semiconductors within the framework of the self-consistent Born approximation. We find that, contrary to the null effect of short-range scattering on spin-Hall current, long-range collisions do produce a nonvanishing contribution to the spin-Hall current, which is independent of impurity density in the diffusive regime and relates only to hole states near the Fermi surface. The sign of this contribution is opposite to that of the previously predicted disorder-independent spin-Hall current, leading to a sign change of the total spin-Hall current as hole density varies. Furthermore, we also make clear that the disorder-independent spin-Hall effect is a result of an interband polarization directly induced by the dc electric field with contributions from all hole states in the Fermi sea., Comment: 9 pages, 1 figure

We employ a quantum Langevin equation approach to establish non-Markovian dynamical equations, on a fully microscopic basis, to investigate the measurement of the state of a coupled quantum dot qubit by a nearby quantum point contact. The ensuing Bloch equations allow us to examine qubit relaxation and decoherence induced by measurement, and also the noise spectrum of meter output current with the help of a quantum regression theorem, at arbitrary bias-voltage and temperature. Our analyses provide a clear resolution of a recent debate concerning the occurrence of a quantum oscillation peak in the noise spectrum., Comment: 5 pages, 3 figures, submitted, published version in Phys. Rev. B

We present a quantum Boltzmann equation analysis of the spin-Hall effect in a diffusive Rashba two-dimensional electron system. Within the framework of the self-consistent Born approximation, we consider the roles of disorder-induced quasiclassical relaxation, collisional broadening of the quasiparticles, and the intracollisional field effect in regard to spin-Hall dynamics. We present an analytical proof that the spin-Hall current vanishes, independently of the coupling strength, of the quasiparticle broadening, of temperature and of the specific form of the isotropic scattering potential. A sum relation of the collision terms in a helicity basis is also examined., Comment: final version, 11 pages, no figure

We explore inelastic cotunneling through a strongly Coulomb-blockaded quantum dot attached to two ferromagnetic leads in the weak coupling limit using a generic quantum Langevin equation approach. We first develop a Bloch-type equation microscopically to describe the cotunneling-induced spin relaxation dynamics, and then develop explicit analytical expressions for the local magnetization, current, and its fluctuations. On this basis, we predict a novel zero-bias anomaly of the differential conductance in the absence of a magnetic field for the anti-parallel configuration, and asymmetric peak splitting in a magnetic field. Also, for the same system with large polarization, we find a negative zero-frequency differential shot noise in the low positive bias-voltage region. All these effects are ascribed to rapid spin-reversal due to underlying spin-flip cotunneling., Comment: 7 pages, 5 figures, submitted

Effects of microwave radiation on magnetoresistance are analyzed in a balance-equation scheme that covers regimes of inter- and intra-Landau level processes and takes account of photon-asissted electron transitions as well as radiation-induced change of the electron distribution for high mobility two-dimensional systems. Short-range scatterings due to background impurities and defects are shown to be the dominant direct contributors to the photoresistance oscillations. The electron temperature characterizing the system heating due to irradiation, is derived by balancing the energy absorption from the radiation field and the energy dissipation to the lattice through realistic electron-phonon couplings, exhibiting resonant oscillation. Microwave modulations of Shubnikov de Haas oscillation amplitude are produced together with microwave-induced resistance oscillations, in agreement with experimental findings. In addition, the suppression of the magnetoresistance caused by low-frequency radiation in the higher magnetic field side is also demonstrated., Comment: 10 pages, 7 figures, published version

In some theoretical analyses of microwave-induced magnetoresistance oscillations in high-mobility two-dimensional systems, the "inelastic relaxation time" $\tau_{in}$ due to electron-electron scattering is evaluated using an equilibrium distribution function $f^0$ in the absence of radiation, and it is concluded that $\tau_{in}$ is much larger than $\tau_{q}$, the single-particle relaxation time due to impurity scattering. However, under the irradiation of a microwave capable of producing magnetoresistance oscillation, the distribution function of the high-mobility electron gas deviates remarkably from $f^0$ at low temperatures. Estimating $\tau_{in}$ using an approximate nonequilibrium distribution function rather than using $f^0$, one will find the system to be in the opposite limit $1/\tau_{in}\ll 1/\tau_{q}$ even for T=0 K. Therefore, models which depend on the assumption $1/\tau_{in}\gg 1/\tau_{q}$ may not be justifiable., Comment: 1 page

We present a two-band kinetic equation method to investigate the anomalous Hall effect in a Rashba two-dimensional electron system subjected to a homogeneous magnetization. The electron-impurity scattering is taken into account in the self-consistent Born approximation. It is demonstrated that the impurity-density-free anomalous Hall conductivity arises from an intrinsic and a disorder-mediated mechanisms, associated respectively with the electron states under and near the Fermi surface. The intrinsic mechanism relates to a dc-field-induced transition process, or in other words, a linear stationary Rabi process. The disorder-mediated one corresponds to a scattering between impurities and the electrons participating in longitudinal transport. Numerically, the dependencies of the anomalous Hall conductivity on the spin-orbit coupling constants and the strength of the magnetization are demonstrated for both the short- and long-range collisions., Comment: 10 pages, 3 figures

We investigate the spin-Hall effect in a two-dimensional heavy-hole system with Rashba spin-orbit coupling using a nonequilibrium Green's function approach. Both the short- and long-range disorder scatterings are considered in the self-consistent Born approximation. We find that, in the case of long-range collisions, the disorder-mediated process leads to an enhancement of the spin-Hall current at high heavy-hole density, whereas for short-range scatterings it gives a vanishing contribution. This result suggests that the recently observed spin-Hall effect in experiment is a result of the sum of the intrinsic and disorder-mediated contributions. We have also calculated the temperature dependence of spin-Hall conductivity, which reveals a decrease with increasing the temperature., Comment: 5 pages, 2 figures, Typos in the values of hole density corrected

We propose a nonequilibrium Green's function approach to study the spin-Hall effect in a two-dimensional electron system with both the Rashba and Dresselhaus spin-orbit couplings. By taking into account the long-range electron-impurity scattering, the derived kinetic equations are solved numerically. It is found the vanishing of the total zero-temperature dissipationless spin-Hall effect, contributing from the intrinsic and disorder-mediated processes. This result has been examined in the wide ranges of spin-orbit coupling constants and electron density., Comment: 5 pages, 1 figure

Recently discovered modulations of Shubnikov-de Haas oscillations in microwave-irradiated two-dimensional electron systems are shown to arise from electron heating induced by the radiation. The electron temperature, obtained by balancing the energy absorption from the microwave field and the energy dissipation to the lattice through realistic electron-phonon couplings, exhibits resonance. The modulation of the Shubnikov de Haas oscillation and the suppression of magnetoresistance are demonstrated together with microwave-induced resistance oscillation, in agreement with experimental findings., Comment: Revised version, published in Appl. Phys. Letters