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Bing Dong

Publications and source records attributed to Bing Dong.

66 records · Page 4Linked to original sources
arXiv2004

Shot noise in resonant tunneling through an interacting quantum dot with intradot spin-flip scattering

In this paper, we present theoretical investigation of the zero-frequency shot noise spectra in electron tunneling through an interacting quantum dot connected to two ferromagnetic leads with possibility of spin-flip scattering between the two spin states by means of the recently developed bias-voltage and temperature dependent quantum rate equations. For this purpose, a generalization of the traditional generation-recombination approach is made for properly taking into account the coherent superposition of electronic states, i.e., the nondiagonal density matrix elements. Our numerical calculations find that the Fano factor increases with increasing the polarization of the two leads, but decreases with increasing the intradot spin-flip scattering.

cond-mat.mes-hall↗
arXiv2004

Time-dependent resonant tunneling for a parallel-coupled double quantum dots

We derive the quantum rate equations for an Aharonov-Bohm interferometer with two vertically coupled quantum dots embedded in each of two arms by means of the nonequilibrium Green's function in the sequential tunneling regime. Basing on these equations, we investigate time-dependent resonant tunneling under a small amplitude irradiation and find that the resonant photon-assisted tunneling peaks in photocurrent demonstrate a combination behavior of Fano and Lorentzian resonances due to the interference effect between the two pathways in this parallel configuration, which is controllable by threading the magnetic flux inside this device.

cond-mat.mes-hall↗
arXiv2004

Photon-Phonon-assisted tunneling through a single-molecular quantum dot

Based on exactly mapping of a many-body electron-phonon interaction problem onto a one-body problem, we apply the well-established nonequilibrium Green function technique to solve the time-dependent phonon-assisted tunneling at low temperature through a single-molecular quantum dot connected to two leads, which is subject to a microwave irradiation field. It is found that in the presence of the electron-phonon interaction and the microwave irradiation field, the time-average transmission and the nonlinear differential conductance display additional peaks due to pure photon absorption or emission processes and photon-absorption-assisted phonon emission processes. The variation of the time-average current with frequency of the microwave irradiation field is also studied.

cond-mat.mes-hall↗
arXiv2003

Quantum rate equations for electron transport through an interacting system in the sequential tunneling regime

We present a set of modified quantum rate equations, with the help of the nonequilibrium Green's function and slave-particle techniques along with the correct quantization, for description of the quantum transport through an interacting mesoscopic region connected with two leads, in the sequential tunneling regime. The assumption that only leading order of $|V|^2$ ($V$ is the tunneling coupling between the interacting central region and the leads) has been taken into account in deriving these equations implies that the quantum rate equations are only valid in the case of weak coupling between the central region and the leads. For demonstrations, we consider two special cases in the central region, a single interacting quantum dot (SQD) with weak spin-flip scattering and a weakly coupled double quantum dots (CQD), as examples. In the limit of zero temperature and large bias voltage, the resulting equations are identical to the previous results derived from the many-body Schrödinger equation. The numerical simulations reveal: 1) the dependence of the spin-flip scattering on the temperature and bias voltage in the SQD; and 2) the possible negative differential conductance and negative tunnel magnetoresistance in the CQD, depending on the hopping between the two quantum dots.

cond-mat.mes-hall↗
arXiv2003

Spin-polarized transport through a quantum dot coupled to ferromagnetic leads: Kondo correlation effect

We investigate the linear and nonlinear transport through a single level quantum dot connected to two ferromagnetic leads in Kondo regime, using the slave-boson mean field approach for finite on-site Coulomb repulsion. We find that for antiparallel alignment of the spin orientations in the leads, a single zero-bias Kondo peak always appears in the voltage-dependent differential conductance with peak height going down to zero as the polarization grows to P=1. For parallel configuration, with increasing polarization from zero, the Kondo peak descends and greatly widens by the appearance of shoulders, and finally splits into two peaks on both sides of the bias voltage around $P\sim 0.7$ until disappears at even larger polarization strength. At any spin orientation angle $θ$, the linear conductance generally drops with growing polarization strength. For a given finite polarization, the minimum linear conductance always appears at $θ=π$.

cond-mat↗
arXiv2003

Quantum transport through double-dot Aharonov-Bohm interferometry in Coulomb blockade regime

Transport through two quantum dots laterally embedded in Aharonov-Bohm interferometry with infinite intradot and arbitrary interdot Coulomb repulsion is analyzed in the weak coupling and Coulomb blockade regime. By employing the modified quantum rate equations and the slave-boson approach, we establish a general dc current formula at temperatures higher than the Kondo temperature for the case that the spin degenerate levels of two dots are close to each other. We examine two simple examples for identical dots - no doubly occupied states and no empty state. In the former, completely destructive coherent transport and phase locking appear at magnetic flux $Φ=Φ_{0}/2$ and $Φ=0$ respectively; in the latter, partially coherent transport exhibits an oscillation with magnetic flux having a period of $Φ_0$.

cond-mat.mes-hall↗
arXiv2003

Kondo-type transport through an interacting quantum dot coupled to ferromagnetic leads

We investigate the equilibrium and out-of-equilibrium Kondo effects in a single-level interacting quantum dot connected to two ferromagnetic leads. Within the non-crossing approximation, we calculate the total density of states (DOS), the linear conductance, and the nonlinear differential conductance for both the parallel and the anti-parallel alignments of the spin polarization orientation in the leads, followed by a brief discussion regarding the validity of this approach. Numerical calculations show that for the anti-parallel alignment, a single Kondo peak always appears in the equilibrium DOS, resulting in the conventional temperature behavior in the linear conductance and the zero-bias maximum in the differential conductance. The strength of the DOS peak is gradually suppressed with increasing polarization, due to the fact that formation of the Kondo-correlated state is more difficult in the presence of higher polarization. On the contrary, for the parallel configuration the Kondo peak in the DOS descends precipitately and splits into two peaks to form a very steep valley between them. This splitting contributes to the appearance of a "hump" in the temperature-dependent linear conductance and a nonzero-bias maximum in the differential conductance. Moreover, application of a bias voltage can split each Kondo peak into two in the nonequilibrium DOS for both configurations. Finally we point out that the tunnel magnetoresistance could be an effective tool to demonstrate the different Kondo effects in different spin configurations found here.

cond-mat.mes-hall↗
arXiv2002

Effect of the Kondo correlation on thermopower in a Quantum Dot

In this paper we study the thermopower of a quantum dot connected to two leads in the presence of Kondo correlation by employing a modified second-order perturbation scheme at nonequilibrium. A simple scheme, Ng's ansatz [Phys. Rev. Lett. {\bf 76}, 487 (1996)], is adopted to calculate nonequilibrium distribution Green's function and its validity is further checked with regard to the Onsager relation. Numerical results demonstrate that the sign of the thermopower can be changed by tuning the energy level of the quantum dot, leading to a oscillatory behavior with a suppressed magnitude due to the Kondo effect. We also calculate the thermal conductance of the system, and find that the Wiedemann-Franz law is obeyed at low temperature but violated with increasing temperature, corresponding to emerging and quenching of the Kondo effect.

cond-mat.mes-hall↗
arXiv2002

Nonequilibrium Kondo Effect in a Multi-level Quantum Dot near singlet-triplet transition

The linear and nonlinear transport through a multi-level lateral quantum dot connected to two leads is investigated using a generalized finite-$U$ slave-boson mean field approach. For a two-level quantum dot, our calculation demonstrates a substantial conductance enhancement near the degeneracy point of the spin singlet and triplet states, a non-monotonic temperature-dependence of conductance and a sharp dip and nonzero bias maximum of the differential conductance. These agree well with recent experiment observations. This two-stage Kondo effect in an out-of-equilibrium situation is attributed to the interference between the two energy levels.

cond-mat.mes-hall↗
arXiv2002

Kondo effect and anti-ferromagnetic correlation in transport through tunneling-coupled double quantum dots

We propose to study the transport through tunneling-coupled double quantum dots (DQDs) connected in series to leads, using the finite-$U$ slave-boson mean field approach developed initially by Kotliar and Ruckenstein [Phys. Rev. Lett. {\bf 57}, 1362 (1986)]. This approach treats the dot-lead coupling and the inter-dot tunnelling $t$ nonperturbatively at arbitrary Coulomb correlation $U$, thus allows the anti-ferromagnetic exchange coupling parameter $J=4t^2/U$ to appear naturally. We find that, with increasing the inter-dot hopping, the DQDs manifest three distinct physical scenarios: the Kondo singlet state of each dot with its adjacent lead, the spin singlet state consisting of local spins on each dot and the doubly occupied bonding orbital of the coupled dots. The three states exhibit remarkably distinct behavior in transmission spectrum, linear and differential conductance and their magnetic-field dependence. Theoretical predictions agree with numerical renormalization group and Lanczos calculations, and some of them have been observed in recent experiments.

cond-mat.mes-hall↗
arXiv2002

Effect of the Kondo correlation on Shot Noise in a Quantum Dot

The current noise in a quantum dot coupled to two leads is investigated in the Kondo regime with and without the influence of magnetic fields by employing a finite-$U$ slave-boson mean field theory to calculate the current-current correlation function at zero temperature. The numerical results show that, depending on the energy level of the QD the Coulomb interactin may reduce or enhance the zero-frequency shot noise power spectrum in comparison with that without Coulomb interaction. But the Fano factor is always reduced significantly due to the Kondo-correlation effect, and the most pronounced suppression appears at the electron-hole symmetry case $2ε_d+U=0$. In addition, the application of a magnetic field enhance the Fano factor of the shot noise at small external voltage, which is attributed to the reduction of the Kondo-enhanced density-of-state and transmission probability in a quantum dot.

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