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1.
We investigate Andreev reflection (AR) tunneling through a ferromagnet-quantum dot-superconductor (F-QD-S) system in the presence of an external ac field. The intradot spin-flip scattering in the QD is involved. Using the nonequilibrium Green function and BCS quasiparticle spectrum for superconductor, time-averaged AR conductance is formulated. The competition between the intradot spin-flip scattering and photon-assisted tunneling dominates the resonant behaviors of the time-averaged AR conductance. For weak intradot spin-flip scattering strengths, the AR conductance shows a series of equal interval resonant levels. However, the single-peak at main resonant level develops into a well-resolved double-peak resonance at a strong intradot spin-flip scattering strength. Remarkable, multiple-photon-assisted tunneling that generates photonic sideband peaks with a variable interval has been found. In addition, the AR conductance-bias voltage characteristic shows a transition between the single-peak to double-peak resonance as the ratio of the two tunneling strengths varies. 相似文献
2.
L. Qin Y. Guo 《The European Physical Journal B - Condensed Matter and Complex Systems》2007,58(4):395-403
We present a theoretical study of the spin-dependent conductance
spectra in a FM/semiconductor quantum-dot (QD)/FM system. Both the
Rashba spin-orbit (SO) coupling in the QD and spin-flip scattering
caused by magnetic barrier impurities are taken into account. It
is found that in the single-level QD system with parallel magnetic
moments in the two FM leads, due to the interference between
different tunneling paths through the spin-degenerate level, a dip
or a narrow resonant peak can appear in the conductance spectra,
which depends on the property of the spin-flip scattering. When
the magnetizations of the two FM leads are noncollinear, the
resonant peak can be transformed into a dip. The Rashba SO
coupling manifests itself by a Rashba phase factor, which changes
the phase information of every tunneling path and can greatly
modulate the conductance. When the QD has multiple levels, the
Rashba interlevel spin-flip effect appears, which changes the
topological property of the structure. Its interplay with the
Rashba phase can directly tune the coupling strengths between dot
and leads, and can result in switching from resonance into
antiresonance in the conductance spectra. 相似文献
3.
By employing the nonequilibrium Green's function, we investigate the spin-dependent linear Andreev reflection (AR) resonant tunneling through a quantum dot connected to a ferromagnetic lead and a superconducting lead, where the magnetization direction in the ferromagnetic lead can be tuned by one. We focus our attention on the effects of the magnetic fields on the AR conductance. One high conductance peak and one low conductance peak are developed in the linear AR conductance when a stronger magnetic field is considered. The interplay between the spin-flip scattering and the magnetic fields on the AR conductance are also studied. 相似文献
4.
Zhen-Gang Zhu 《Physics letters. A》2008,372(5):695-699
Selective and large polarization of current injected into semiconductor (SC) is predicted in ferromagnet (FM)/quantum dot (QD)/SC system by varying the gate voltage above the Kondo temperature. In addition, spin-dependent Kondo effect is also revealed below Kondo temperature. It is found that Kondo resonances for up spin state are suppressed with increasing of the polarization P of the FM lead. While the down one is enhanced. The Kondo peak for up spin is disappear at P=1. 相似文献
5.
We theoretically studied the spin-dependent charge transport in a two-dimensional electron gas with Dresselhaus spin-orbit coupling (DSOC) and metal junctions. It is shown that the DSOC energy can be directly measured from the tunneling conductance spectrum. We found that spin polarization of the conductance in the propagation direction can be obtained by injecting from the DSOC system. We also considered the effect of the interfacial scattering barrier (both spin-flip and non-spin-flip scattering) on the overall conductance and the spin polarization of the conductance. It is found that the increase of spin-flip scattering can enhance the conductance under certain conditions. Moreover, both types of scattering can increase the spin polarization below the branches crossing of the energy band. 相似文献
6.
We report a study of spin-dependent transport through a quantum dot irradiated by continuous circularly polarized light resonant to the electron-heavy hole transition. We use the nonequilibrium Green's function to calculate the spin accumulation, spin-resolved currents, and current polarization in the presence of an external bias and intradot Coulomb interaction. It is found that for a range of external biases sign reversal of the current polarization can be modulated. The system thus operates as a rectifier for spin current polarization. This effect follows from the interplay between the external irradiation and the Coulomb repulsion. The spin-polarized transport through a three-terminal device is also discussed. Spin current with high polarization could be obtained due to spin filter effect. 相似文献
7.
H.-K. Zhao J. Wang Q. Wang 《The European Physical Journal B - Condensed Matter and Complex Systems》2006,51(3):425-433
We have investigated the mesoscopic transport through the system
with a quantum dot (QD) side-coupled to a toroidal carbon nanotube
(TCN) in the presence of spin-flip effect. The coupled QD
contributes to the mesoscopic transport significantly through
adjusting the gate voltage and Zeeman field applied to the QD.
The compound TCN-QD microstructure is related to the separate
subsystems, the applied external magnetic fields, as well as the
combination of subsystems. The spin current component Izs is
independent on time, while the spin current components Ixs and
Iys evolve with time sinusoidally. The rotating magnetic field
induces novel levels due to the spin splitting and photon
absorption procedures. The suppression and enhancement of resonant
peaks, and semiconductor-metal phase transition are observed by
studying the differential conductance through tuning the
source-drain bias and photon energy. The magnetic flux induces
Aharonov-Bohm oscillation, and it controls the tunnelling behavior
due to adjusting the flux. The Fano type of multi-resonant
behaviors are displayed in the conductance structures by
adjusting the gate voltage Vg and the Zeeman field
applied to the QD. 相似文献
8.
By means of the nonequilibrium Green function technique, the effect of spin-flip scatterings on the spin-dependent electrical transport in ferromagnet–insulator–ferromagnet (FM–I–FM) tunnel junctions is investigated. It is shown that Jullière's formula for the tunnel conductance must be modified when including the contribution from the spin-flip scatterings. It is found that the spin-flip scatterings could lead to an angular shift of the tunnel conductance, giving rise to the junction resistance not being the largest when the orientations of magnetizations in the two FM electrodes are antiparallel, which may offer an alternative explanation for such a phenomenon observed previously in experiments in some FM–I–FM junctions. The spin-flip assisted tunneling is also observed. 相似文献
9.
We investigate mesoscopic transport through a system that consists of a central quantum dot (QD) and two single-wall
carbon nanotube (SWCN) leads in the presence of a rotating
magnetic field. The spin-flip effect is induced by the rotating
magnetic field, and the tunnelling current is sensitively related
to the spin-flip effect. We present the calculations of charge
and spin current components to show the intimate relations to the
SWCN leads. Zeeman effect is important when the applied magnetic
field is strong enough. The current characteristics are quite
different when the source-drain bias is zero (eV=0) and nonzero
(eV≠0). The asymmetric peak and valley of spin current versus
gate voltage exhibit Fano resonance. Multi-resonant peaks of spin
current versus photon energy ħω reflect the structure
of CN quantum wires, as well as the resonant photon absorption and
emission effect. The matching-mismatching of channels in the CN
leads and QD results in novel spin current structure by tuning the
frequency. 相似文献
10.
We investigate theoretically the electronic transport through a parallel-coupled double quantum dot (DQD) molecule attached to metallic electrodes, in which the spin-flip scattering on each quantum dot is considered. Special attention is paid to the effects of the intradot spin-flip processes on the linear conductance by using the equation of motion approach for Green’s functions. When a weak spin-flip scattering on each quantum dot is present, the single Fano peak splits into two Fano peaks, and the Breit–Wigner resonance may be suppressed slightly. When the spin-flip scattering strength on each quantum dot becomes strong, the linear conductance spectrum consists of two Breit–Wigner peaks and two Fano peaks due to the quantum interference effects. The positions and shapes of these resonant peaks can be controlled by using the magnetic flux through the quantum device. 相似文献
11.
We investigate the spin accumulation in a double quantum dot Aharonov-Bohm (AB) interferometer in which both the Rashba spin-orbit (RSO) interaction and intradot Coulomb interaction are taken into account. Due to the existence of the RSO interaction, the electron, flowing through different arms of the AB ring, will acquire a spin-dependent phase factor in the tunnel-coupling strengths. This phase factor will induce various interesting interference phenomena. It is found that the electrons of the different spin directions can accumulate in the two dots by properly adjusting the bias and the intradot level with a fixed RSO interaction strength. Moreover, both the magnitude and direction of the spin accumulation in each dot can be conveniently controlled and tuned by the gate voltage acting on the dot or the bias on the lead. 相似文献
12.
DONG Zheng-Chao 《理论物理通讯》2004,41(1):135-140
The tunneling conductance and tunneling magnetoresistance (TMR) are
investigated in ferromagnet/insulator/ferromagnet/insulator/d-wave
superconductor (FM/I/FM/I/d-wave SC) structures by applying an extended
Blonder-Tinkham-Klapwijk (BTK) approach. We study the effects of the
exchange splitting in the FM, the magnetic impurity scattering in the thin
insulator interface of FM/I/FM, and noncollinear magnetizations in adjacent
magnetic layers on the TMR. It is shown (1) that the tunneling conductance
and TMR exhibit amplitude-varying oscillating behavior with exchange
splitting, (2) that with the presence of spin-flip scattering in insulator
interface of FM/I/FM, the TMR can be dramatically enhanced, and (3)
that the TMR depends strongly on the angle between the magnetization of two
FMs. 相似文献
13.
《Solid State Communications》2006,137(1-2):53-58
We investigate the spin-flip effect on electronic transport in a nanostructure composed of two nonmagnetic (NM) leads separated by a periodic spacer. The spacer is composed of one-dimensional heterostructure formed by a sequence of magnetic (A) and nonmagnetic (B) sites periodically juxtaposed (as in a typical periodic quantum dot (QD)). The calculations are based on the tight-binding model and transfer matrix method, which compute the current–voltage characteristic within the Landauer–Büttiker formalism. Our main goal is to assess the contribution of the spin-flip scattering to the transport properties of such systems. The spin-dependent transport behavior can be controlled via a gate magnetic field and an applied voltage in the ballistic regime. Our results show that the conductance strongly depends on the configurations of the magnetic QD. The application of the predicted results may be useful in designing spin-valve devices, such as spin-polarized molecular transistors. 相似文献
14.
With the aid of the nonequilibrium Green's function and the Lang-Firsov canonical transformation, we investigate the joint effects of a phononic environment and the spin-flip scattering on the Andreev reflection (AR) in a ferromagnet/single-molecular quantum dot/superconductor (FM/MQD/SC) system. In the presence of the strong electron-phonon interaction (EPI), it is found that the EPI strongly suppresses the AR current (called the Franck-Condon blockade). When the coherent spin-flip (similar to a transverse magnetic field) is taken into account within the MQD, the AR current is significantly enhanced, furthermore, the spin-polarized AR current or even the pure spin-polarized AR current can be generated. By tuning the system parameters, the amplitude and direction of the AR current can be changed, this provides an efficient mechanism for controlling the AR process. 相似文献
15.
C. Jiang X. F. Xie W. J. Gong G. Z. Wei 《The European Physical Journal B - Condensed Matter and Complex Systems》2010,75(2):237-245
Nonequilibrium electron and spin transport properties in a
parallel double quantum dot (QD) Fano interferometer are
theoretically studied. With the shift of gate voltage around the
chemical potential of either lead, we find the Fano lineshapes in
the differential conductance spectra, which is sensitively
determined by the bias voltage strength and appropriate QD level
distributions. The intradot Coulomb interactions modulate the Fano
interference in a substantial way and can induce the emergence of
negative differential conductance, because of its nontrivial role in
splitting the QD levels. In the presence of a local Rashba
spin-orbit coupling, the interplay between the magnetic and Rashba
fields induces the occurrence of the nonequilibrium spin-related
Fano interference, different from the linear-transport results.
Furthermore, the striking Coulomb-driven spin accumulation in the
‘resonant-channel’ QD appears. 相似文献
16.
We have studied the thermoelectric properties through ferromagnetic leads-QD coupled system (F-QD-F) in the Kondo regime by nonequilibrium Green's functions method. The spin-flip effect induced by ferromagnetic leads and Kondo effect influence the thermoelectric properties significantly. The peak-valley structure emerges at the low temperature due to Kondo resonance, and the peak-valley structure also relies on the polarization angle θ, the spin-dependent linewidth function Γγσ and the energy level of QD εd. Novel resonant peak also emerges in the curve of ZTc versus polarization angle θ. The Kondo effect suppresses the figure of merit ZTc and the spin-dependent figure of merit ZTs. In addition, the spin-dependent figure of merit ZTs is relate with the gap between Γγ↑ and Γγ↓. 相似文献
17.
Relaxation of a nonequilibrium state in a disordered metal with a spin-dependent electron energy distribution is considered.
The collision integral due to the electron-electron interaction is computed within the approximation of a two-quasiparticle
scattering. It is shown that the spin-flip scattering processes with a small energy transfer may lead to the divergence of
the collision integral for a quasi one-dimensional wire. This divergence is present only for a spin-dependent electron energy
distribution that corresponds to the total electron spin magnetization M = 0 and only for nonzero interaction in the triplet channel. In this case, a nonperturbative treatment of the electron-electron
interaction is needed to provide an effective infrared cutoff. 相似文献
18.
Relaxation of a nonequilibrium state in a disordered metal with a spin-dependent electron energy distribution is considered.
The collision integral due to the electron-electron interaction is computed within the approximation of a two-quasiparticle
scattering. It is shown that the spin-flip scattering processes with a small energy transfer may lead to the divergence of
the collision integral for a quasi one-dimensional wire. This divergence is present only for a spin-dependent electron energy
distribution that corresponds to the total electron spin magnetization M = 0 and only for nonzero interaction in the triplet channel. In this case, a nonperturbative treatment of the electron-electron
interaction is needed to provide an effective infrared cutoff.
The text was submitted by the authors in English.
An erratum to this article is available at . 相似文献
19.
Resonant Andreev reflection in a normal-metal/quantum-dot/superconductor system with coupled Majorana bound states 下载免费PDF全文
Andreev reflection(AR) in a normal-metal/quantum-dot/superconductor(N–QD–S) system with coupled Majorana bound states(MBSs) is investigated theoretically. We find that in the N–QD–S system, the AR can be enhanced when coupling to the MBSs is incorporated. Fano line-shapes can be observed in the AR conductance spectrum when there is an appropriate QD–MBS coupling or MBS–MBS coupling. The AR conductance is always e~2/2h at the zero Fermi energy point when only QD–MBSs coupling is considered. In addition, the resonant AR occurs when the MBS–MBS coupling roughly equals to the QD energy level. We also find that an AR antiresonance appears when the QD energy level approximately equals to the sum of the QD–MBS coupling and the MBS–MBS coupling. These features may serve as characteristic signatures for the probe of MBSs. 相似文献
20.
Based on the nonequilibrium Green' function method, the spin-dependent Fano effect through parallel-coupled double quantum dots has been investigated by taking account of both Rashba spin-orbit interaction and intradot Coulomb interaction. It is shown that the quantum interference through the bonding, antibonding states and through their Coulomb blockade counterparts may result in two Breit-Wigner resonances and two Fano resonances in the conductance spectra. Moreover, the Fano lineshape of the two spin components can be modulated by Rashba spin-orbit interaction when the magnetic flux is switched on. 相似文献