共查询到20条相似文献,搜索用时 22 毫秒
1.
We study the spin-dependent electron transport through parallel coupled quantum dots (QDs) embedded in an Aharonov-Bohm (AB) interferometer connected asymmetrically to leads. Both the Rashba spin-orbit interaction (RSOI) inside one of the QDs, which acquires a spin-dependent phase factor in the tunnel-coupling strengths when the electrons flow through this arm of the AB ring, and an inhomogeneous magnetic flux penetrating the structure are taken into account. Due to the existence of the RSOI induced phase factor, magnetic flux and the interdot coupling, a spin-dependent Fano effect will arise. We pay special attention on the properties of the local density of states and the conductance when the electron phase factor is close to integer multiplies of a quantum of flux. It is shown that the roles and lifetimes of the bonding and antibonding states of the two spin components are very sensitive to the phase factor and can be well controlled accordingly. This manipulation of the spin degree of freedom relies on the existence of RSOI but can be fulfilled even when its strength is very weak. The proposed structure can be easily realized with present technology and might be of practical applications in spintronics devices and quantum computing. 相似文献
2.
Persistent current and transmission probability in the Aharonov-Bohm (AB) ring with an embedded quantum dot (QD) are studied using the technique of the scattering matrix. For the first time, we find that the persistent current can arise in the absence of magnetic flux in the ring with an embedded QD. The persistent current and the transmission probability are sensitive to the lead-ring coupling and the short-range potential barrier. It is shown that increasing the lead-ring coupling or the short-range potential barrier causes the suppression of the persistent current and the increasing resonance width of the transmission probability. The effect of the potential barrier on the number of the transmission peaks is also investigated. The dependence of the persistent current and the transmission probability on the magnetic flux exhibits a periodic property with period of the flux quantum. 相似文献
3.
The electron transport through an Aharonov-Bohm (AB) interferometer with embedded four coupled quantum dots (QDs) is studied with the Green's function technique. The QDs are coupled to each other by the hopping integral tc. Two among them connect with the left lead and the other two with the right lead by the tunneling matrix element T which incorporates the effects of the applied magnetic field φ. The linear conductance spectra swap between the molecular levels and the atomic states by adjusting tc and T. Fano effect appears when the electrons tunnel through different channels contributed by different QDs energy levels, and the Fano resonance peaks split for large tc. The Fano factor can be manipulated by tc, T, φ, and the QD energy levels. 相似文献
4.
He Gao 《Physics letters. A》2008,372(35):5695-5700
We have investigated the mesoscopic transport properties of a quantum dot embedded Aharonov-Bohm (AB) interferometer applied with a rotating magnetic field. The spin-flip effect is induced by the rotating magnetic field, and the tunneling current is sensitive to the spin-flip effect. The spin-flipped electrons tunneling from the direct channel and the resonant channel interfere with each other to form spin-polarized tunneling current components. The non-resonant tunneling (direct transmission) strength and the AB phase φ play important roles. When the non-resonant tunneling (background transmission) exists, the spin and charge currents form asymmetric peaks and valleys, which exhibit Fano-type line shapes by varying the source-drain bias voltage, or gate voltage. The AB oscillations of the spin and charge currents exhibit distinct dependence on the magnetic flux and direct tunneling strength. 相似文献
5.
W. Y. Cui S. Z. Wu G. Jin X. Zhao Y. Q. Ma 《The European Physical Journal B - Condensed Matter and Complex Systems》2007,59(1):47-54
We investigate the electron transmission through a structure of
serial mesoscopic metallic rings coupled to two external leads. A
set of analytical expressions based on the quantum waveguide
transport and the transfer matrix method are derived and used to
discuss the effects of geometric configurations on transmission
probabilities. It is found that in the contact ring case the
existence of an applied magnetic flux is necessary to create
transmission gaps, while in the non-contact ring case transmission
gaps always appear irrespective of whether there is an applied
magnetic flux or not. The transmissions for periodic rings with a
defect ring and periodic rings built by two sorts of rings are
also briefly studied. It is also found that the transmission
periodicity with wave vector must be ensured by the
commensurability of two characteristic lengths, i.e., of the half
perimeter of a ring and the connecting wire between two adjacent
rings. The special points of wave vector and magnetic flux which
give rise to the transmission resonance and antiresonance are
analyzed in detail. 相似文献
6.
Santanu K. Maiti 《Physics letters. A》2009,373(48):4470-4474
We explore AND gate response in a double quantum ring where each ring is threaded by a magnetic flux ?. The double quantum ring is attached symmetrically to two semi-infinite one-dimensional metallic electrodes and two gate voltages, namely, Va and Vb, are applied, respectively, in the lower arms of the two rings which are treated as two inputs of the AND gate. The system is described in the tight-binding framework and the calculations are done using the Green's function formalism. Here we numerically compute the conductance-energy and current-voltage characteristics as functions of the ring-to-electrode coupling strengths, magnetic flux and gate voltages. Our study suggests that, for a typical value of the magnetic flux ?=?0/2 (?0=ch/e, the elementary flux-quantum) a high output current (1) (in the logical sense) appears only if both the two inputs to the gate are high (1), while if neither or only one input to the gate is high (1), a low output current (0) results. It clearly demonstrates the AND gate behavior and this aspect may be utilized in designing an electronic logic gate. 相似文献
7.
Using the tight-binding approximation and the transfer matrix
method, this paper studies the electronic transport properties
through a periodic array of quantum-dot (QD) rings threaded by a
magnetic flux. It demonstrates that the even--odd parity of the QD
number in a single ring and the number of the QD rings in the array
play a crucial role in the electron transmission. For a single QD
ring, the resonance and antiresonance transmission depend not only
on the applied magnetic flux but also on the difference between the
number of QDs on the two arms of the ring. For an array of QD rings,
the transmission properties are related not only to the even--odd
parity of the number $N_{0}$ of QDs in the single ring but also to
the even--odd parity of the ring number $N$ in the array. When the
incident electron energy is aligned with the site energy, for the
array of $N$ rings with $N_{0}={\rm odd}$ the antiresonance
transmission cannot occur but the resonance transmission may occur
and the transmission spectrum has $N$ resonance peaks ($N-1$
resonance peaks) in a period for $N={\rm odd}$ (for $N={\rm even}$).
For the array of $N$ rings with $N_{0}={\rm even}$ the transmission
properties depend on the flux threading the ring and the QD number
on one arm of the ring. These results may be helpful in designing
QD devices. 相似文献
8.
In this Letter, we studied the electronic transport through a parallel-coupled double quantum dot (DQD) molecule including impurity effects at zero temperature. The linear conductance can be calculated by using the Green's function method. An obvious Fano resonance arising from the impurity state in the quantum dot is observed for the symmetric dot-lead coupling structure in the absence of the magnetic flux through the quantum device. When the magnetic flux is presented, two groups of conductance peaks appear in the linear conductance spectra. Each group is decomposed into one Breit-Wigner and one Fano resonances. Tuning the system parameters, we can control effectively the shapes of these conductance peaks. The Aharonov-Bohm (AB) oscillation for the magnetic flux is also studied. The oscillation period of the linear conductance with π, 2π or 4π may be observed by tuning the interdot tunneling coupling or the dot-impurity coupling strengths. 相似文献
9.
We discuss the influence of nanostructure geometry on the thermoelectric properties in quantum ring consists of one QD in each arm, each QD connects with side QD. The calculations are based on the time-dependent Hamiltonian model, the steady state is considered to obtain an analytical expression for the transmission probability as a function of system energies. We employed the transmission probability to calculate the thermoelectric properties. We investigate thermoelectric properties through three configurations of this nanostructure. Figure of merit enhanced in configuration (II) when side QD connected to upper arm of quantum ring. The magnetic flux threads quantum ring. The effect of magnetic flux on the thermoelectric properties is examined. 相似文献
10.
提出了中臂弯曲的多臂量子环模型,且是上臂最短和下臂最长的不等臂量子环.研究发现:总磁通为零时,持续电流随半导体环增大发生非周期性振荡,并与电极的磁矩方向及隧穿电子的自旋方向相关,下臂因为最长而获得最小的平均持续电流.AB磁通增强时,持续电流会发生周期性振荡,各臂之间明显出现相互制约的现象.各臂持续电流之间的差异与臂长和磁通分布相关,Rashba自旋轨道耦合具有改变持续电流相位和相位差的效应.在一定条件下,两种波函数所对应的持续电流是可分离的.
关键词:
多臂量子环
持续电流
Rashba自旋轨道耦合 相似文献
11.
The electronic transport properties of fractal quantum waveguide networks in the presence of a magnetic field are studied. A Generalized Eigen-function Method (GEM) is used to calculate the transmission and reflection coefficients of the studied systems unto the fourth generation Sierpinski fractal network with node number N=123. The relationship among the transmission coefficient T, magnetic flux Φ and wave vector k is investigated in detail. The numerical results are shown by the three-dimensional plots and contour maps. Some resonant-transmission features and the symmetry of the transmission coefficient T to flux Φ are observed and discussed, and compared with the results of the tight-binding model. 相似文献
12.
Spin-polarized transport through an Aharonov–Bohm ring containing two quantum dots (QDs) in each of its arms is studied by using the nonequilibrium Green’s function technique. We take both the Rashba spin-orbit interaction that exists in one of the QDs, and an inhomogeneous magnetic flux penetrating through the ring, into consideration. It is found that a 100% spin-polarized current can be driven out of the QDs ring, and both the spin directions and the magnitude of the outgoing current can be controlled. The origin of the pure spin-up or spin-down current is interpreted in terms of the spin accumulation in the QDs. This device is realizable by presently available technologies and can be used as a spin filter. 相似文献
13.
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
14.
A mesoscale Aharonov-Bohm (AB) ring with a quantum dot (QD) embedded in each arm is computationally modeled for unique transmission properties arising from a combination of AB effects and Zeeman splitting of the QD energy levels. A tight-binding Hamiltonian is solved, providing analytical expressions for the transmission as a function of system parameters. Transmission resonances with spin-polarized output are presented for cases involving either a perpendicular field, or a parallel field, or both. The combination of the AB-effect with Zeeman splitting allows sensitive control of the output resonances of the device, manifesting in spin-polarized states which separate and cross as a function of applied field. In the case with perpendicular flux, the AB-oscillations exhibit atypical non-periodicity, and Fano-type resonances appear as a function of magnetic flux due to the flux-dependent shift in the QD energy levels via the Zeeman effect. 相似文献
15.
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
16.
S.-G. Cheng Y. X. Xing X. C. Xie Q.-F. Sun 《The European Physical Journal B - Condensed Matter and Complex Systems》2009,67(4):551-557
The Josephson current through an Aharonov-Bohm (AB)
interferometer, in which a quantum dot (QD) is situated on one arm
and a magnetic flux Φ threads through the ring, has been
investigated. In the presence of the magnetic flux, the relation
between the Josephson current and the superconductor phase is
complex, and the system can be adjusted to π junction by either
modulating the magnetic flux or the QD’s energy level
εd. Due to the electron-hole symmetry, the Josephson
current I has the property
I(εd,Φ)=I(-εd,Φ+π). The Josephson
current exhibits a jump when a pair of Andreev bound states aligns
with the Fermi energy. The condition for the current jump is given.
Particularly, we find that the position of the current jump and the
position of the maximum value of the critical current Ic are
identical. Due to the interference between the two paths, the
critical current Ic versus the QD’s level εd shows a
typical Fano shape, which is similar to the Fano effect in the
corresponding normal device. However they also show some
differences. For example, the critical current never reaches zero
for any parameters, while the current in the normal device can reach
zero at the destruction point. 相似文献
17.
Yong-Jian Xiong 《Physica B: Condensed Matter》2008,403(17):2671-2675
We investigate a one-dimensional mesoscopic ring with a constant magnetic flux coupled to an electron reservoir which is driven by an oscillating potential. There is time-dependent tunneling current between the ring and reservoir with a zero net value. The persistent current in the ring is also time-dependent due to the driving potential. The time-averaged persistent current is related to electron transfer between two coupled parts which is associated with the Fermi energy and side bands of the reservoir. 相似文献
18.
D. N. Son N. ArboledaJr W. A. Dino H. Kasai 《The European Physical Journal B - Condensed Matter and Complex Systems》2007,57(1):27-35
We consider a two-terminal Aharonov-Bohm (AB) interferometer with a quantum dot inserted in one path of the AB ring.
We investigate the transport properties of this system in and out of the Kondo regime. We utilize perturbation theory to
calculate the electron self-energy of the quantum dot with respect to the intradot Coulomb interaction. We show the expression
of the Kondo temperature as a function of the AB phase together with its dependence on other characteristics such as the
linewidth of the ring and the finite Coulomb interaction and the energy levels of the quantum dot. The current oscillates
periodically as a function
of the AB phase. The amplitude of the current oscillation decreases with increasing Coulomb interaction. For a given temperature,
the electron transport through the AB interferometer
can be selected to be in or out of the Kondo regime by changing the magnetic flux threading perpendicular to the AB ring of
the system. 相似文献
19.
Kondo Resonance versus Fano Interference in Double Quantum Dots Coupled to a Two-Lead One-Ring System
下载免费PDF全文
![点击此处可从《中国物理快报》网站下载免费的PDF全文](/ch/ext_images/free.gif)
We analyse the transport properties of a coupled double quantum dot (DQD) device with one of the dots (QD1) coupled to metallic leads and the other (QD2) embedded in an Aharonov-Bhom (A-B) ring by means of the slaveboson mean-field theory. It is found that in this system, the Kondo resonance and the Fano interference exist simultaneously, the enhancing Kondo effect and the increasing hopping of the QD2-Ring destroy the localized electron state in the QD2 for the QD1-leads, and accordingly, the Fano interference between the DQD-leads and the QD1-leads are suppressed. Under some conditions, the Fano interference can be quenched fully and the single Kondo resonance of the QD1-leads comes into being. Moreover, when the magnetic flux of the A-B ring is zero, the influence of the parity of the A-B ring on the transport properties is very weak, but this influence becomes more obvious with non-zero magnetic flux. Thus this model may be a candidate for future device applications. 相似文献
20.
Spin-polarized quantum transport through an Aharonov--Bohm quantum-dot-ring 总被引:1,自引:0,他引:1
下载免费PDF全文
![点击此处可从《中国物理》网站下载免费的PDF全文](/ch/ext_images/free.gif)
In this paper the quantum transport through an Aharonov--Bohm (AB)
quantum-dot-ring with two dot-array arms described by a single-band
tight-binding Hamiltonian is investigated in the presence of
additional magnetic fields applied to the dot-array arms to produce
spin flip of electrons. A far richer interference pattern than
that in the charge transport alone is found. Besides the usual AB
oscillation the tunable spin polarization of the current by the
magnetic flux is a new observation and is seen to be particularly
useful in technical applications. The spectrum of transmission
probability is modulated by the quantum dot numbers on the up-arc and down-arc
of the ring, which, however, does not affect the period of the AB
oscillation. 相似文献