The electronic transport in a system of two quantum rings side-coupled to a quantum wire is studied via a single-band tunneling tight-binding Hamiltonian. We derived analytical expressions for the conductance and spin polarization when the rings are threaded by magnetic fluxes with Rashba spin-orbit interaction. We show that by using the Fano and Dicke effects this system can be used as an efficient spin-filter even for small spin orbit interaction and small values of magnetic flux. We compare the spin-dependent polarization of this design and the polarization obtained with one ring side coupled to a quantum ring. As a main result, we find better spin polarization capabilities as compared to the one ring design
We consider the electronic transport through a Rashba quantum dot coupled to ferromagnetic leads. We show that the interference of localized electron states with resonant electron states leads to the appearance of the Fano-Rashba effect. This effect occurs due to the interference of bound levels of spin-polarized electrons with the continuum of electronic states with an opposite spin polarization. We investigate this Fano-Rashba effect as a function of the applied magnetic field and Rashba spin-orbit coupling.
The electronic transport through a parallel double quantum-dot molecule attached asymmetrically to leads is studied under a magnetic field. We model the system by means of a non interacting two-impurity Anderson Hamiltonian. We find that the conductance shows Fano and Dicke effects that can be controlled by the magnetic flux.
We predict the occurrence of Fano lineshapes in a semiconductor quantum wire with local spin-orbit (Rashba) coupling. We show that the Rashba interaction acts in a strictly one dimensional channel as an attractive impurity, leading to the formation of purely bound states. In a quasi-one dimensional system these bound states couple to the conduction ones through the Rashba intersubband mixing, giving rise to pronounced dips in the linear conductance plateaus. We give exact numerical results and propose an approximate model capturing the main ingredients of the effect.
We study the interference of two tunable Rashba regions in a quantum wire with one propagating mode. The transmission dips (Fano-Rashba dips) of the two regions either cross or anti cross depending on the distance between the two regions. For large separations we find Fabry-Pérot oscillations due to the interference of forwards and backwards propagating modes. At small separations overlapping evanescent modes play a prominent role, leading to an enhanced transmission and destroying the conductance dip. Analytical expressions in scattering-matrix theory are given and the relevance of the interf…
We analyze the linear conductance of a semiconductor quantum wire containing a region where a local Rashba spin-orbit interaction is present. We show that Fano lineshapes appear in the conductance due to the formation of quasi bound states which interfere with the direct transmission along the wire, a mechanism that we term the Fano-Rashba effect. We obtain the numerical solution of the full Schrödinger equation using the quantum-transmitting-boundary method. The theoretical analysis is performed using the coupled-channel model, finding an analytical solution by ansatz. The complete numerical …
The single photon transport through a one dimensional array of cavities is studied theoretically. Analytical expressions of the reflection and transmission are given. The transmission shows an energy spectrum with forbidden and allowed bands that depends on the detuning parameter of the system. We show that the allowed miniband is formed due to the indirect coupling between the atoms in each cavity. In addition, the band edges can be controlled by the degree of detuning of the level of the atoms. We discuss the analogy between this phenomenon with the Fano and Dicke effects.
We investigate theoretically the effect of a time dependent oscillating potential on the transport property of the Dirac Fermion through a monolayer graphene electrostatic barrier under the influence of the Rashba spin orbit interaction. The time dependent problem is solved in the frame work of the non perturbative Floquet approach. It is noted that the dynamic condition of the barrier may be controlled by tuning the Rashba parameter. Introduction of the spin orbit interaction causes splitting of the Fano resonance(FR), a characteristic feature in photon assisted tunneling. The separation betw…
We investigate the electronic transport in a quantum wire with localized Rashba interaction. The Rashba field forms quasi-bound states which couple to the continuum states with an opposite spin direction. The presence of this Rashba dot causes Fano-like antiresonances and dips in the wire's linear conductance. The Fano lineshape arises from the interference between the direct transmission channel along the wire and the hopping through the Rashba dot. Due to the confinement, we predict the observation of large charging energies in the local Rashba region which lead to Coulomb-blockade effects i…
We propose a scheme of spin transistor using a $T$-shaped structure with local Rashba interaction. A wide antiresonance energy gap appears due to the interplay of two types of interference, the Fano-Rashba interference and the structure interference. A large current from the gap area can be obtained via changing the Rashba strength and/or the length of the sidearm by using gate voltage. The robustness of the antiresonance gap against strong disorder is demonstrated and shows the feasibility of this structure for the real application.
We theoretically study electronic transport through a region with inhomogeneous Rashba spin-orbit (RSO) coupling placed between two normal regions in a monolayer graphene. The inhomogeneous RSO region is characterized by linearly varying RSO strength within its borders and constant RSO strength in the central region. We calculate the transmission properties within the transfer matrix approach. It is shown that the amplitude of conductance oscillations reduces and at the same time the magnitude of conductance increases with increasing border thickness. We also investigate how the Fano factor ca…
We report on the quantum interference and spin accumulation on double quantum dots with Rashba spin-orbit coupling and electron-electron interaction, based on the Keldysh nonequilibrium Green function formalism. It is shown that Rashba spin-orbit interaction can strongly affect the conductance spectrum. By gradually increasing the Rashba parameter from zero, Fano resonances in strong overlap regime continuously evolve to resolve antiresonances. This transition is ascribed to the phase shift of couplings between molecular states and the lead due to spin precession. We also show that both bias a…
We consider a single-level quantum dot coupled to two leads which are ferromagnetic in general. Apart from tunneling processes conserving electron spin, we also include processes associated with spin-flip of tunneling electrons, which appear due to Rashba spin-orbit coupling. Charge and heat currents are calculated within the non-equilibrium Green's function technique. When the electrodes are half-metallic (fully spin polarized), the Rashba spin-orbit coupling leads to Fano-like interference effects, which result in an enhanced thermoelectric response. It is also shown that such a system can o…
We investigate theoretically the spin-polarized electron transport for a wide-narrow-wide (WNW) quantum wire under the modulation of Rashba spin-orbit interaction (SOI). The influence of both the structure of the quantum wire and the interference between different pairs of subbands on the spin-polarized electron transport is taken into account simultaneously via the spin-resolved lattice Green function method. It is found that a very large vertical spin-polarized current can be generated by the SOI-induced effective magnetic field at the structure-induced Fano resonance even in the presence of…
We develop a theory of cavity quantum electrodynamics for a 2D electron gas in the presence of Rashba spin-orbit coupling and perpendicular static magnetic field, coupled to spatially nonuniform multimode quantum cavity photon fields. We demonstrate that the lowest polaritonic frequency of the full Hamiltonian can vanish for realistic parameters, achieving the Dicke superradiant quantum phase transition. This singular behaviour originates from soft spin-flip transitions possessing a non-vanishing dipole moment at non-zero wave vectors and can be viewed as a magnetostatic instability.
We analyze the effect of Rashba spin-orbit coupling and of a local tunnel barrier on the persistent spin and charge currents in a one-dimensional conducting Aharonov-Bohm (AB) ring symmetrically coupled to two leads. First, as an important consequence of the spin-splitting, it is found that a persistent spin current can be induced which is not simply proportional to the charge current. Second, a magnification effect of the persistent spin current is shown when one tunes the Fermi energy near the Fano-type antiresonances of the total transmission coefficient governed by the tunnel barrier stren…
In this work, we have studied the spin-dependent ballistic transport and anomalous quantum tunnelling in Bilayer Graphene (BLG) hybrid connected to two Rashba-Zeeman (RZ) leads under an external electric biasing. We investigated the transmission and conductance for the proposed system using scattering matrix formalism and Landauer - Buttiker formula considering a double delta-like barrier under a set of experimentally viable parameters. We found that the transmission characteristics are notably different for up and down spin incoming electrons depending upon the strength of magnetization. More…
We study the spin transport and polarization properties of manganese-doped dual-guanine molecules connected to graphene leads using non-equilibrium Green's function method. It is shown that a manganese doped dual-guanine molecule is a biological semiconductor and behaves as a prefect spin filter. We show that this semiconductor can behave as a spin switch when the Rashba spin-orbit interaction is considered. In addition, it is shown that, a large conductance is observed due to the Fano-Kondo-Rashba resonance effect.
We investigate the transport properties of ballistic quantum wires in the presence of Zeeman spin splittings and a spatially inhomogeneous Rashba interaction. The Zeeman interaction is extended along the wire and produces gaps in the energy spectrum which allow electron propagation only for spinors lying along a certain direction. For spins in the opposite direction the waves are evanescent far away from the Rashba region, which plays the role of the scattering center. The most interesting case occurs when the magnetic field is perpendicular to the Rashba field. Then, the spins of the asymptot…
We study shot noise for spin-polarized currents and entangled electron pairs in a four-probe (beam splitter) geometry with a local Rashba spin-orbit (s-o) interaction in the incoming leads. Within the scattering formalism we find that shot noise exhibits Rashba-induced oscillations with continuous bunching and antibunching. We show that entangled states and triplet states can be identified via their Rashba phase in noise measurements. For two-channel leads we find an additional spin rotation due to s-o induced interband coupling which provides enhanced spin control. We show that the s-o intera…
We investigate the electron transport through a mesoscopic ring side-coupled with a quantum dot(QD) in the presence of Rashba spin-orbit(SO) interaction. It is shown that both the Fano resonance and the spin interference effects play important roles in the electron transport properties. As the QD level is around the Fermi energy, the total conductance shows typical Fano resonance line shape. By applying an electrical gate voltage to the QD, the total transmission through the system can be strongly modulated. By threading the mesoscopic ring with a magnetic flux, the time-reversal symmetry of t…
Numerical methods are developed in the quantum transport calculations for electron in the waveguides with spin-orbital (Rashba) interaction. The methods are based on a hybrid mode-matching scheme in which the wavefunctions are expressed as the superposition of eigenmodes in the lead regions and in the device region the wavefunction is expressed on the discrete basis. Two versions are presented for the lead without and with the Rashba interaction. In the latter case the eigenmodes are obtained from a quadratic eigenproblem calculation. These methods are suitable for the systems with variable ge…
We consider theoretically a $1D$-semiconducting wire with strong Rashba interaction in proximity with $s$-wave superconductor, driven into topological phase by external magnetic field. Additionally, we take into account on-site Coulomb interactions inside the wire. The system is modelled by a tight binding Hamiltonian with Rashba hopping term and induced $s$-wave superconductivity. Calculations are performed utilizing recursive Green's function method, and Coulomb interactions are treated selfconsistently within Hubbard $I$ approximation. For the Hubbard levels residing within $p$-wave superco…
Quantum wires with periodic local Rashba spin-orbit couplings are proposed for a higher performance of spin field-effect transistor. Fano-Rashba quantum interference due to the spin-dependent modulated structure gives rise to a broad energy range of vanishingly small transmission. Tuning Rashba spin-orbit couplings can provide the on- or off-currents with extremely large on/off current ratios even in the presence of a strong disorder.
We investigate the linear conductance of a stripe of spin-orbit interaction in a 2D electron gas; that is, a 2D region of length $\ell$ along the transport direction and infinite in the transverse one in which a spin-orbit interaction of Rashba type is present. Polarization in the contacts is described by means of Zeeman fields. Our model predicts two types of conductance oscillations: Ramsauer oscillations in the minority spin transmission, when both spins can propagate, and Fano oscillations when only one spin propagates. The latter are due to the spin-orbit coupling with quasibound states o…
A graphene $pn$ junction is studied theoretically in the presence of both intrinsic and Rashba spin-orbit couplings. We show that a crossover from perfect reflection to perfect transmission is achieved at normal incidence by tuning the perpendicular electric field. By further studying angular dependent transmission, we demonstrate that perfect reflection at normal incidence can be clearly distinguished from trivial band gap effects. We also investigate how spin-orbit effects modify the conductance and the Fano factor associated with a potential step in both $nn$ and $np$ cases.
We analyse the conductance of the Aharonov-Bohm one-dimensional quantum ring touching a quantum wire. It is shown that in accordance with experimental data the period of the AB oscillations strongly depends on the chemical potential and the Rashba coupling parameter. The dependence of the conductance on the carrier's energy is shown to reveal the Fano resonances.
We review recent studies of the shot noise of spin-polarized charge currents and pure spin currents in multiterminal semiconductor nanostructures, while focusing on the effects brought by the intrinsic Rashba spin-orbit (SO) coupling and/or extrinsic SO scattering off impurities in two-dimensional electron gas (2DEG) based devices. By generalizing the scattering theory of quantum shot noise to include the full spin-density matrix of electrons injected from a spin-filtering electrode, we show how decoherence and dephasing in the course of spin precession can lead to substantial enhancement of t…
The authors investigate quantum transport in a narrow constriction fabricated by narrow band gap semiconductor materials with spin-orbit (SO) couplings. We consider the Rashba-Dresselhaus (RD) spin-orbit interactions (SOIs) and the Zeeman effect induced by an in-plane magnetic field along the transport direction. The interplay of the RD-SOI and the Zeeman effect may induce a SOI-Zeeman gap and influence the transport properties. We demonstrate that an attractive scattering potential may induce electron-like quasi-bound-state feature and manifest the RD-SOI-Zeeman induced Fano line-shape in con…
We present the study of transport properties of a superconducting wire with strong Rashba spin-orbit coupling for different orientations of an external magnetic field. Using the nonequilibrium Green's functions in the tight-binding approach the crucial impact of the relative alignment of lead magnetization and the Majorana bound state (MBS) spin polarization on the low-bias conductance and shot noise is presented. Depending on this factor the transport regime can effectively vary from symmetric to extremely asymmetric. In the last situation the current-symmetry breaking, the suppression of the…
The conductance quantization and shot noise below the first conductance plateau $G_0 = 2e^2/h$ are measured in a quantum point contact fabricated in a GaAs/AlGaAs tunnel-coupled double quantum well. From the conductance measurement, we observe a clear quantized conductance plateau at $0.5G_0$ and a small minimum in the transconductance at $0.7 G_0$. Spectroscopic transconductance measurement reveals three maxima inside the first diamond, thus suggesting three minima in the dispersion relation for electric subbands. Shot noise measurement shows that the Fano factor behavior is consistent with t…
We study transport properties of the helical edge channels of a quantum spin Hall (QSH) insulator, in the presence of electron-electron interactions and weak, local Rashba spin-orbit coupling. The combination of the two allows for inelastic backscattering that does not break time-reversal symmetry (TRS), resulting in interaction-dependent power law corrections to the conductance. Here, we use a non-equilibrium Keldysh formalism to describe the situation of a long, one-dimensional edge channel coupled to external reservoirs, where the applied bias is the leading energy scale. By calculating exp…
The transport properties of a circular billiard with attached channels, which is an open system, have been studied in the presence of the Dresselhaus and Rashba spin-orbit interactions. It has been shown that this interaction leads to the appearance of additional Fano resonances in the energy dependence of the conductance, the width of which is proportional to the fourth power of the spin-orbit coupling constant.
Using the Landauer-Bütikker formalism, we study the graphene magneto-transport in the presence of Rashba spin-orbit interaction (RSOI). We show that the angle resolved transmission probability in the proposed structures can be tuned by the RSOI strength. The transmission spectrum show Klein tunneling in the parallel (P) magnetization configuration which can be blocked by the RSOI. This effect is also observable for the anti-parallel (AP) magnetization configuration in different incident angle. The numerical results shows that the spin-polarized conductance strongly depends on the strength of t…
We generalize the scattering theory of quantum shot noise to include the full spin-density matrix of electrons injected from a spin-filtering or ferromagnetic electrode into a quantum-coherent nanostructure governed by various spin-dependent interactions. This formalism yields the spin-resolved shot noise power for different experimental measurement setups--with ferromagnetic source and ferromagnetic or normal drain electrodes--whose evaluation for the diffusive multichannel quantum wires with the Rashba (SO) spin-orbit coupling shows how spin decoherence and dephasing lead to substantial enha…
We study normal transport and the sub-gap spectrum of superconductor-normal-superconductor (SNS) junctions made of semiconducting nanowires with strong Rashba spin-orbit coupling. We focus, in particular, on the role of confinement effects in long ballistic junctions. In the normal regime, scattering at the two contacts gives rise to two distinct features in conductance, Fabry-Perot resonances and Fano dips. The latter arise in the presence of a strong Zeeman field $B$ that removes a spin sector in the leads (\emph{helical} leads), but not in the central region. Conversely, a helical central r…
System of two quantum dots attached to external electrodes is considered theoretically in orbital Kondo regime. In general, the double dot system is coupled via both Coulomb interaction and direct hoping. Moreover, the indirect hopping processes between the dots (through the leads) are also taken into account. To investigate system's electronic properties we apply slave-boson mean field (SBMF) technique. With help of the SBMF approach the local density of states for both dots and the transmission (as well as linear and differencial conductance) is calculated. We show that Dicke- and Fano-like …
