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1.
The Kondo effect and the Andreev reflection tunneling through a normal (ferromagnet)-double quantum dots-superconductor hybrid system is examined in the low temperature by using the nonequilibrium Green's function technique in combination with the slave-boson mean-field theory. The interplay of the Kondo physics and the Andreev bound state physics can be controlled by varying the interdot hopping strength. The Andreev differential conductance is mainly determined by the competition between Kondo states and Andreev states. The spin-polarization of the ferromagnetic electrode increases the zero-bias Kondo peak. The spin-flip scattering influences the Kondo effect and the Andreev reflection in a nontrivial way. For the ferromagnetic electrode with sufficiently large spin polarization, the negative Andreev differential conductance is found when the spin flip strength in the double quantum dots is sufficiently strong. 相似文献
2.
The spin current in a parabolically confined semiconductor
heterojunction quantum wire with Dresselhaus spin--orbit coupling is
theoretically studied by using the perturbation method. The formulae
of the elements for linear and angular spin current densities are
derived by using the recent definition for spin current based on spin
continuity equation. It is found that the spin current in this
Dresselhaus spin--orbit coupling quantum wire is antisymmetrical,
which is different from that in Rashba model due to the difference in
symmetry between these two models. Some numerical examples for the
result are also demonstrated and discussed. 相似文献
3.
AC field-controlled Andreev tunneling through two serially-coupled quantum dots are investigated theoretically by using the nonequilibrium Green's function method. The photon-assisted Andreev tunneling is studied in detail. It is found that the average current depends distinctly on the interdot coupling. In the weak interdot coupling case, the average current versus the gate voltage exhibit negative peaks on the left-hand side and positive peaks on the right-hand side of the Fermi level. However, in the strong interdot coupling case, the current exhibit both negative and positive peaks on each side of the Fermi level. Furthermore, the system can function as an electron pump capable of transporting electrons through the resonant photon-assisted Andreev tunneling. 相似文献
4.
Electron transport for a laser-irradiated quantum channel with Rashba spin--orbit coupling 下载免费PDF全文
We investigate theoretically the electron transport for a two-level
quantum channel (wire) with Rashba spin--orbit coupling under the
irradiation of a longitudinally-polarized external laser field at low
temperatures. Using the method of equation of motion for Keldysh
nonequilibrium Green function, we examine the time-averaged spin
polarized conductance for the system with photon polarization
parallel to the wire direction. By analytical analysis and a few
numerical examples, the interplay effects of the external laser field
and the Rashba spin--orbit coupling on the spin-polarized conductance
for the system are demonstrated and discussed. It is found that the
longitudinally-polarized laser field can adjust the spin polarization
rate and produce some photon sideband resonances of the conductance
for the system. 相似文献
5.
Ben-Yuan Gu Yao Lu Tzong-Jer Yang 《The European Physical Journal B - Condensed Matter and Complex Systems》2002,26(4):493-502
We present numerical investigations of the transmission properties of electrons in a normal quantum wire tangentially attached
to a superconductor ring threaded by magnetic flux. A point scatterer with a δ -function potential is placed at node to model
scattering effect. We find that the transmission characteristics of electrons in this structure strongly depend on the normal
or superconducting state of the ring. The transmission probability as a function of the energy of incident electrons, in the
case of a superconductor ring threaded by one quantum magnetic flux, emerges one deep dip, imposed upon the first broad bump
in spectrum. This intrinsic conductance dip originates from the superconductor state of the ring. When increasing the magnetic
flux from one quantum magnetic flux to two, the spectrum shifts toward higher energy region in the whole. This conductance
dip accordingly shifts and appears in the second bump. In the presence of a point-scatterer at the node, the spectrum is substantially
modified. Based on the condition of the formation of the standing wave functions in the ring and the broken of the time-reserve
symmetry of Schr?dinger equation after switching magnetic flux, the characteristics of transmission of electrons in this structure
can be well understood.
Received 6 November 2001 相似文献
6.
We investigate the shot noise of electron transport through an Aharonov-Casher ring subject to the Rashba spin-orbit coupling (SOC). Analytic expressions for the coefficients of reflection and transmission are derived by using the Griffith boundary conditions. For this kind of SOC, the ballistic transport of electrons can be analyzed as two independent spin channels, and both of them have the same transmission and reflection coefficients. The dependences of shot noise and Landauer-Biittiker conductance on controllable factors, including the strength of Rashba SOC, the asymmetrical angle of lead-connection positions, the radius of the rings, and the wave vector (or energy) of the incident Fermi electrons, are explicitly described by some new combined parameters. The ways that the shot noise and conductance vary with Rashba SOC and with asymmetrical angle are demonstrated by numerical simulations, respectively. It is revealed that the shot noise reaches its maximum for the particular situation of half transmission and half reflection and zero shot noise occurs at conductance maxima. 相似文献
7.
Intrinsic Hall effect and separation of Rashba and Dresselhaus spin splittings in semiconductor quantum wells 下载免费PDF全文
We have proposed a method to separate Rashba and Dresselhaus spin splittings in
semiconductor quantum wells by using the intrinsic Hall effect. It is shown that the
interference between Rashba and Dresselhaus terms can deflect the electrons in
opposite transverse directions with a change of sign in the macroscopic Hall
current, thus providing an alternative way to determine the different contributions
to the spin--orbit coupling. 相似文献
8.
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
9.
The effect of a kink on the conductance of a nanoscale polymer molecular wire is theoretically investigated on the basis of the Su–Schrieffer–Heeger (SSH) model combined with the Green's function formalism. It is found that, due to the appearance of kink, the molecular conductance decreases rapidly with the molecular length and reaches near zero when the molecular length is over a critical value. The reason is attributed to the localized effect of kink on the electronic state at the Fermi energy. The effect of electron-lattice coupling strength on the conductance is also discussed. 相似文献
10.
Maria A. Davidovich E. V. Anda C. A. Büsser G. Chiappe 《Physica B: Condensed Matter》2002,320(1-4):366-369
The T=0 transport properties of a wire interacting with a lateral two-level quantum dot are studied by using an exact numerical calculation. The wire conductance, the spin–spin correlation and the Kondo temperature are obtained as a function of the dot level energy spacing. When the dot has two electrons and spin SD1, the wire current is totally quenched by the S=1 Kondo effect. The Kondo temperature is maximum at the singlet–triplet transition and its dependence upon the dot energy spacing follows a non-universal scaling law. 相似文献
11.
The influence of the Dresselhaus spin--orbit coupling on the tunnelling magnetoresistance in ferromagnet/ insulator /semiconductor/ insulator /ferromagnet tunnel junctions 下载免费PDF全文
This paper investigates the effect of Dresselhaus spin--orbit
coupling on the spin-transport properties of
ferromagnet/insulator/semiconductor/insulator/ferromagnet
double-barrier structures. The influence of the thickness of the
insulator between the ferromagnet and the semiconductor on the
polarization is also considered. The obtained results indicate that
(i) the polarization can be enhanced by reducing the insulator
layers at zero temperature, and (ii) the tunnelling magnetoresistance
inversion can be illustrated by the influence of the Dresselhaus
spin--orbit coupling effect in the double-barrier structure. Due to
the Dresselhaus spin--orbit coupling effect, the tunnelling
magnetoresistance inversion occurs when the energy of a localized
state in the barrier matches the Fermi energy EF of the
ferromagnetic electrodes. 相似文献
12.
Xing-Tao An 《Physics letters. A》2008,372(8):1313-1318
Based on the scattering approach, we investigate transport properties of electrons in a one-dimensional waveguide that contains a ferromagnetic/semiconductor/ferromagnetic heterojunction and tunnel barriers in the presence of Rashba and Dresselhaus spin-orbit interactions. We simultaneously consider significant quantum size effects, quantum coherence, Rashba and Dresselhaus spin-orbit interactions and noncollinear magnetizations. It is found that the tunnel barrier plays a decisive role in the transmission coefficient and shot noise of the ballistic spin electron transport through the heterojunction. When the small tunnel barriers are considered, the transport properties of electrons are quite different from those without tunnel barriers. 相似文献
13.
研究了连接在正常金属电极和超导电极之间的耦合Majorana束缚态(MBSs)T形双量子点结构中的Andreev反射.研究发现,对于T形双量子点结构,当入射能量等于边耦合量子点能级时Andreev反射电导出现Fano振荡,连接MBSs之后,零费米能附近出现一对新的Fano型振荡峰.如果忽略两个MBSs之间的相互作用,零费米能点的Andreev反射电导为定值1/2G_0(G_0=2e~2/h),不受量子点能级、双量子点之间耦合强度以及量子点与MBSs之间的耦合强度的影响.此外,在没有耦合MBSs的T形双量子点结构中,调节双量子点间的耦合强度可以使零费米能附近的Andreev反射电导出现由共振带向反共振带的转变,而耦合MBSs之后,又可以使反共振消失转而出现新的共振峰. 相似文献
14.
The dependence of the optical absorption spectrum of a semiconductor quantum well on two-dimensional electron concentration n(e) is studied using CdTe samples. The trion peak (X-) seen at low n(e) evolves smoothly into the Fermi edge singularity at high n(e). The exciton peak (X) moves off to high energy, weakens, and disappears. The X,X- splitting is linear in n(e) and closely equal to the Fermi energy plus the trion binding energy. For Cd0.998Mn0.002Te quantum wells in a magnetic field, the X,X- splitting reflects unequal Fermi energies for M = +/-1/2 electrons. The data are explained by Hawrylak's theory of the many-body optical response including spin effects. 相似文献
15.
In this paper, conductance of spin and electron in graphene-based ferromagnet—superconductor (FS) and parallel and antiparallel ferromagnet–superconductor–ferromagnet (FSF) junctions are studied. Using the Dirac–Bogoliubov–de Gennes equations, Andreev and normal reflections are obtained and then using these coefficients, conductance of spin and electrons are calculated at the FS interface(s) analytically. As a result, both the energy dependence of spin and charge differential conductances are investigated and a comparison between electron and spin transport is done in this paper. Effect of exchange energy of ferromagnet h on conductances is studied too. 相似文献
16.
The quantum conductance for electrons scattering from a uniform scatterer in a narrow-wire semiconductor is calculated. Instead of getting the conductance directly from the calculation of transmission coefficient, we calculate the reflection coefficient instead. The transmission coefficient is then calculated by using the conservation law, T=I−R. This alternative method can avoid the instability of the conductance obtained by including more evanescent modes for a finite-range scatterer in a narrow-wire semiconductor. This method is applied to a semi-infinite strip potential barrier and a rectangular potential barrier in a narrow wire. The quantum stepwise conductance is obtained in both cases. For a repulsive rectangular potential barrier, there are oscillations in each stepwise conductance. For an attractive rectangular potential barrier, there exist multiple quasi-bound states below the sub-band energies which can cause the drop of the quantum conductance. The effect of the continuum quasi-bound states diminishes as the energy of the incident electron increases, but the influence of the discrete quasi-bound states still persists. 相似文献
17.
Matveev KA 《Physical review letters》2004,92(10):106801
We study the effect of Coulomb interactions on the conductance of a single-mode quantum wire connecting two bulk leads. When the density of electrons in the wire is very low, they arrange in a finite-length Wigner crystal. In this regime the electron spins form an antiferromagnetic Heisenberg chain with an exponentially small coupling J. An electric current in the wire perturbs the spin chain and gives rise to a temperature-dependent contribution of the spin subsystem to the resistance. At low temperature TJ the spin effect reduces the conductance to e2/h. 相似文献
18.
Modulation of Spin Distribution and Spin Transport by a Magnetic Field in a Quasi-One-Dimensional System with Spin--Orbit Coupling 下载免费PDF全文
The distributions of spin and currents modulated by magnetic field in a transverse parabolic confined two-dimensional electronic system with a Rashba spin--orbit coupling have been studied numerically. It is shown that the spin accumulation and the spin related current are generated by magnetic field if the spin--orbit coupling is presented. The distributions of charge and spin currents are antisymmetrical along the cross-section of confined system. A transversely applied electric field does not influence the characteristic behaviour of charge- and spin-dependent properties. 相似文献
19.
Z.-Y. Zhang 《The European Physical Journal B - Condensed Matter and Complex Systems》2008,63(1):65-69
Along the lines of Blonder, Tinkham and Klapwijk, we investigate
the charge transport through ferromagnet/two-dimensional
electronic gas/d-wave superconductor (F/2DEG/S) junctions in the
presence of Rashba spin-orbit (SO) coupling and focus our
attention on the interplay between spin polarization and spin
precession. At zero spin polarization, the spin-mixing scattering
resulted from Rashba SO coupling decreases the zero-bias
conductance peak. Under spin polarization, spin precession
introduces novel Andreev reflection, which competes with the
effect of spin-mixing scattering. If the F layer is a half metal,
the later effect is overwhelmed by that of novel Andreev
reflection. As a result, the zero-bias conductance dip caused by
spin polarization is enhanced, and at strong Rashba SO coupling, a
split zero-bias peak is found in the gap. In an intermediate
region where the two effects are comparable with each other, the
zero-bias conductance shows a reentrant behavior as a function of
Rashba SO coupling. 相似文献
20.
Maslyuk VV Bagrets A Meded V Arnold A Evers F Brandbyge M Bredow T Mertig I 《Physical review letters》2006,97(9):097201
Using density functional theory we perform theoretical investigations of the electronic properties of a freestanding one-dimensional organometallic vanadium-benzene wire. This system represents the limiting case of multidecker Vn(C6H6)(n+1) clusters which can be synthesized with established methods. We predict that the ground state of the wire is a 100% spin-polarized ferromagnet (half-metal). Its density of states is metallic at the Fermi energy for the minority electrons and shows a semiconductor gap for the majority electrons. We find that the half-metallic behavior is conserved up to 12% longitudinal elongation of the wire. Ab initio electron transport calculations reveal that finite size vanadium-benzene clusters coupled to ferromagnetic Ni or Co electrodes will work as nearly perfect spin filters. 相似文献