Rashba Spin-orbit Interaction Research Articles

Interband optical absorption coefficient of the diluted magnetic semiconductor ellipsoid quantum dot with Rashba spin orbit interaction

Interband optical absorption coefficient of the diluted magnetic semiconductor ellipsoid quantum dot with Rashba spin orbit interaction

Uncovering bound states in the continuum in InSb nanowire networks

Bound states in the continuum (BICs) are exotic, localized states even though their energy lies in the continuum spectra. Since its discovery in 1929, the quest to unveil these exotic states in charge transport experiments remains an active pursuit in condensed matter physics. Here, we study charge transport in InSb nanowire networks in the ballistic regime and subject to a perpendicular magnetic field as ideal candidates to observe and control the appearance of BICs. We find that BICs reveal themselves as distinctive resonances or antiresonances in the conductance by varying the applied magnetic field and the Fermi energy. We systematically consider different lead connections in hashtag-like nanowire networks, finding the optimal configuration that enhances the features associated with the emergence of BICs. Finally, the investigation focuses on the effect of the Rashba spin–orbit interaction of InSb on the occurrence of BICs in nanowire networks. While the interaction generally plays a detrimental role in the signatures of the BICs in the conductance of the nanowire networks, it opens the possibility to operate these nanostructures as spin filters for spintronics. We believe that this work could pave the way for the unambiguous observation of BICs in charge transport experiments and for the development of advanced spintronic devices.

Spin dynamics of 2-DEG Rashba-Dresselhaus spin-orbit systems: Quantum propagators and semi-analytical analysis in low electron density.

Abstract The spin dynamics in space and time for Dresselhaus and Rashba spin-orbit interaction 2-DEG systems can be studied for any value of their β and α coefficients by using quantum propagators. With the development of analytical expressions for the quantum propagators and numerical solutions of the wave function, it has been possible to simulate the spin propagation in space-time and analyze the spin dynamics for different α/β ratios. In the present paper, the effects of the spin diffusion for large collision time τp, was performed by using quantum propagators for different α/β ratios. It was found that the largest degree of spin polarization is achieved when |α| = |β|.

Engineered Josephson diode effect in kinked Rashba nanochannels

The superconducting diode effect, reminiscent of the unidirectional charge transport in semiconductor diodes, is characterized by a nonreciprocal, dissipationless flow of Cooper pairs. This remarkable phenomenon arises from the interplay between symmetry constraints and the inherent quantum behavior of superconductors. Here, we explore the geometric control of the diode effect in a kinked nanostrip Josephson junction based on a two-dimensional electron gas (2DEGs) with Rashba spin-orbit interaction. We provide a comprehensive analysis of the diode effect as a function of the kink angle and the out-of-plane magnetic field. Our analysis reveals a rich phase diagram, showcasing a geometry and field-controlled diode effect. The phase diagram also reveals the presence of an anomalous Josephson effect related to the emergence of trivial zero-energy Andreev bound states, which can evolve into Majorana bound states. Our findings indicate that the exceptional synergy between geometric control of the diode effect and topological phases can be effectively leveraged to design and optimize superconducting devices with tailored transport properties.

The magnetization in the lattice of quantum rings with rashba spin-orbit interaction

The magnetic properties of the lattice formed by noninteracting semiconductor quantum rings in a longitudinal magnetic field are investigated. It was shown that when the value of the Rashba parameter ξ = 1.5, the magnetization varies from positive to negative with changes in the Aharonov–Bohm flux and amplitude oscillations decrease.

The role of Rashba spin-orbit induced spin textures in the anomalous Josephson effect

This work reports the theoretical investigation into the mechanism underpinning the anomalous Josephson effect within ballistic systems; currently, there is no agreed-upon microscopic mechanism behind the origin of this effect. The prototypical system we study is a ballistic two-dimensional junction containing a two-dimensional Rashba spin-orbit interaction. In this paper, we demonstrate how this two-dimensional Rashba interaction mixes the spins of adjacent transverse subbands, leading to significant spin-asymmetry within the junction. Under an external magnetic field, applied perpendicular to both the axis of transport and the normal vector of the junction, the sinusoidal Josephson current can then experience an anomalous phase shift. The role of this spin mixing in the limit of a single sub-band is initially explored by deriving an analytical expression for the resulting anomalous phase shift. The analysis is then extended to systems with multiple occupied sub-bands; in this later section, starting from a microscopic model, we derive an analytic formula for the resulting anomalous phase shift indicating it is linear in both magnetic field and spin-orbit strength. We then verify and validate all findings by comparing them with numerical results evaluated by a tight-binding model.

Inhomogeneous stripe phase and tunable Majorana zero modes in Rashba s-wave superconducting systems in the presence of in-plane Zeeman field

Based on the extended Bogoliubov–de Gennes theory, the inhomogeneous stripe order and Majorana bound states are demonstrated in s-wave superconducting systems with Rashba spin–orbit interaction when the in-plane Zeeman field is applied. For a fully open square sample, topological phase transitions can be driven by the Zeeman field, and the stripe phase with spatially oscillating order parameter shows up across a critical field strength. The topological channels arise in this phase, which can be utilized to create and manipulate Majorana zero modes. Interestingly, (quasi-)one-dimensional channels with diminished pairing amplitude can be formed in narrow arms of a square loop, accompanied by the reconstruction of energy spectra of the condensate and the realization of robust Majorana zero-energy states at the ends of channels. The associated evolution of topological phases and the location of Majorana zero modes are highly sensitive to the field direction. Moreover, the effects of the rectangular aspect-ratio and the off-centered hole as well as the surface defects on Majorana end modes are explored in Rashba asymmetric loops. In comparison, the field-dependent evolution processes of low-energy levels behave more complicated because the emergence of confined topological channels can be effectively tuned by the length and width of loop arms as well as the size and position of an introduced small indentation at the outer edge. Rich patterns of Majorana corner-like states are generated for such asymmetric systems. Our theoretical predictions may shed new light on the tunability of Majorana zero modes and provide useful guidance for future experiments and applications.

Spin/valley dependent dwell time in an 8-Pmmn borophene junction

Spin/valley dependent dwell time in 8-Pmmn borophene junction under Rashba spin–orbit interaction (RSOI) is studied. The dwell time as well as transmission probability for incident electrons with spin-up show a different behavior than the incident electrons with spin-down, and these quantities can be controlled effectively by the junction direction, incident angle, the RSOI strength and the barrier width. Also, the dwell time is dependent on the degree of freedom of the valley and shows oscillating behavior with the increase of the barrier width. The spin polarization and spin filtering in 8-Pmmn borophene junction under RSOI can be obtained in the time domain.

Analytical study of magnetic properties of quantum dot/ring system: Rashba, magnetic field, and electron-electron effects

Abstract Magnetic behavior of a two-electron quantum dot/ring system are analytically studied with electron-electron (e-e) interaction taking into account the Rashba spin-orbit interaction (SOI) and magnetic field. The Jacobi transformation has been employed to separate the Hamiltonian of the system to the center of mass and relative terms. The Schrödinger equation is analytically solved, and energy spectra are obtained. Then, the magnetization and susceptibility are calculated. The magnetization decreases by rising the magnetic field without and with SOI and also without e-e interaction. Also, SOI slightly modifies the magnetization of the system without e-e interaction. The susceptibility displays a peak structure as the magnetic field changes from low values to high values. The susceptibility by considering e-e interaction and without SOI is always negative and its value decreases by rising the magnetic field. The susceptibility displays a transition from diamagnetic to paramagnetic with e-e interaction and SOI.

Supercurrent and Superconducting Diode Effect in Parallel Double Quantum Dots with Rashba Spin-Orbit Interaction.

We study theoretically the supercurrent and the superconducting diode effect (SDE) in a structure comprising parallel-coupled double quantum dots (DQDs) sandwiched between two superconductor leads in the presence of a magnetic flux. The influence of the Rashba spin-orbit interaction (RSOI), which induces a spin-dependent phase factor in the dot-superconductor coupling strength, is taken into account by adopting the nonequilibrium Green's function technique. This RSOI-induced phase factor serves as a driving force for the supercurrent in addition to the usual superconducting phase difference, and it leads to the system's left/right asymmetry. Correspondingly, the magnitude of the positive and negative critical currents become different from each other: the so-called SDE. Our results show that the period, magnitude, and direction of the supercurrents depend strongly on the RSOI-induced phase factor, dots' energy levels, interdot coupling strengths, and the magnetic flux. In the absence of magnetic flux, the diode efficiency is negative and may approach -2, which indicates the perfect diode effect with only negative flowing supercurrent in the absence of a positive one. Interestingly enough, both the sign and magnitude of the diode efficiency can be efficiently adjusted with the help of magnetic flux, the dots' energy levels and the interdot coupling strength and thus provide a controllable SDE by rich means, such as gate voltage or host materials of the system.

GaAs quantum transport: Scrutinizing the effects of pressure, temperature and Rashba-Dresselhaus spin-orbit interactions for next-generation spintronic devices

This research investigates the spin-dependent transmission attributes and associated Giant Magnetoresistance (GMR) effect emerging from spin-polarized electron tunneling in a GaAs quantum well superlattice (QWS). The influence of Rashba and Dresselhaus spin-orbit interactions (SOIs) on transport properties is analyzed under the framework of the scattering matrix method. Our quantitative findings revealed that these spin-orbit couplings (SOCs) introduce inherent spin-filtering mechanisms, significantly influencing transmission probabilities. Furthermore, numerical estimations proved that external perturbations including pressure, temperature and structural modifications considerably impact the quantum transport characteristics of the scrutinized system. Additionally, major outcomes suggest that precise manipulation of spin-dependent transport in GaAs QWS holds promise for advancing spintronics technology. It is found that with well-tuned parameter values, the SOCs behave as a spin-dependent barrier modifying the band shape and its anisotropy. This study offers novel insights into the fundamental physics governing spin-dependent transport within quantum superlattices with promising implications for the development of advanced spintronic devices.

Effects of magnetic field on the Rashba spin–orbit interaction in an asymmetry quantum well

Effects of magnetic field on the Rashba spin–orbit interaction in an asymmetry quantum well

Role of confinement shape and spin-orbit interactions on binding energy, temperature, transition energy, susceptibility and oscillator strength of an off-center [formula omitted] impurity in a GaAs quantum dot

This study explores the influence of confinement potential shape on the behavior of an off-center D0 impurity in a quantum dot (QD). In this study, we use the power exponential potential and Rashba spin-orbit interaction (RSOI), and Dresselhaus spin-orbit interaction (DSOI) beside an external magnetic field. Employing the variational method, we obtained the ground and first excited state energies and corresponding binding energies, transition energy, and magnetic susceptibilities across various impurity positions, QD parameters, and potential shapes. We ascertain the stable temperature by equating the maximum binding energy of an off-center D0 system. Subsequently, we computed the oscillator strength (OS) and conducted a comparative analysis with existing literature. Our findings demonstrate an exciting behavior in response to changes in potential shape, QD parameters, and spin-orbit coupling strengths. It helps us better understand how an off-center impurity behaves with different potential shapes in QDs and helps engineers to design devices in spintronics.

Conductance, spin and valley polarizations through 8-Pmmn borophene magnetic barriers

Conductance, spin and valley polarizations through 8-Pmmn borophene barriers in the presence of external Rashba spin–orbit interaction (RSOI) and magnetic field are investigated theoretically. The spin-dependent conductance shows a strong dependence on the direction of the 8-Pmmn borophene barriers, the strength of RSOI and value of the magnetic field strength. For two barriers unlike to one barrier, the spin-dependent conductance exhibits a prominent oscillatory behavior. For the parallel configuration, the dependence of conductance on the magnetic field is more than for the antiparallel configuration. Transmission probability without and with spin rotation decreases drastically with the increase in the value of the magnetic field, so that for sufficiently large magnetic fields, the transmission probability is zero for most electron incidence angles. The size and direction of the spin and valley polarization can be tuned by the strength of RSOI, direction of the 8-Pmmn borophene barriers, size of the magnetic field and type of parallel or antiparallel configuration. In certain conditions, full valley polarization can be achieved in the proposed structure.

Josephson Diode Effect in Parallel-Coupled Double-Quantum Dots Connected to Unalike Majorana Nanowires.

We study theoretically the Josephson diode effect (JDE) when realized in a system composed of parallel-coupled double-quantum dots (DQDs) sandwiched between two semiconductor nanowires deposited on an s-wave superconductor surface. Due to the combined effects of proximity-induced superconductivity, strong Rashba spin-orbit interaction, and the Zeeman splitting inside the nanowires, a pair of Majorana bound states (MBSs) may possibly emerge at opposite ends of each nanowire. Different phase factors arising from the superconductor substrate can be generated in the coupling amplitudes between the DQDs and MBSs prepared at the left and right nanowires, and this will result in the Josephson current. We find that the critical Josephson currents in positive and negative directions are different from each other in amplitude within an oscillation period with respect to the magnetic flux penetrating through the system, a phenomenon known as the JDE. It arises from the quantum interference effect in this double-path device, and it can hardly occur in the system of one QD coupled to MBSs. Our results also show that the diode efficiency can reach up to 50%, but this depends on the overlap amplitude between the MBSs, as well as the energy levels of the DQDs adjustable by gate voltages. The present model is realizable within current nanofabrication technologies and may find practical use in the interdisciplinary field of Majorana and Josephson physics.

Thermodynamic properties of [formula omitted] double quantum wire in the presence of impurity and Rashba spin-orbit interaction

We investigate the effects of impurities and Rashba spin-orbit interaction on the thermodynamic properties in the InxGa1−xN double quantum wire. The energy and eigenvectors of our system are obtained through analytical diagonalization in the presence of external fields, Rashba spin-orbit interaction, and impurities. These energy levels are used to analyse the entropy, mean energy, heat capacity, and free energy of the InxGa1−xN double quantum wire. The system's entropy increases with temperature and Rashba spin-orbit interaction but decreases with impurity. At low temperatures, entropy appears weakly dependent on impurity and exhibits minimal dependence on it. The heat capacity shows a peak structure and rises as impurity and the Rashba spin-orbit interaction increase at low temperatures. At low temperatures, the system's mean energy gradually increases. As the temperature rises, the mean energy becomes independent of interaction strength and increases more rapidly. The mean energy decreases with increasing impurity and Rashba spin-orbit interaction. The thermodynamic properties of our system, such as entropy, heat capacity, mean energy, and free energy, make it suitable for applications in electronics (such as the fabrication of energy storage devices and transistors), industry (such as the operation of magnetic levitation trains), and medicine (such as MRI).

Spin-dependent shot noise in 8-Pmmn borophene based-superlattice

The effect of the Rashba spin-orbit interaction on the shot noise, spin/valley polarization in 8-Pmmn borophene-based superlattice are studied theoretically, by applying the transfer-matrix approach. The spin-dependent transmission probability can be easily controlled by the number of superlattice barriers, the strength of the Rashba, and the incident electron angle. The Fano factor without spin rotation as well as with spin rotation shows an oscillatory pattern versus the strength of the Rashba, and the oscillatory behavior becomes more pronounced as the number of barriers increases. Also, the Fano factor shows a strong dependence on the superlattice direction and number of barriers. The spin and valley polarizations can be easily controlled by the number of barriers and the direction of superlattice. Our findings in this work could provide useful for valleytronics/spintronics systems based on the 8-Pmmn borophene.

Two-electron conduction band of a graphene quantum dot and coherent spin manipulation

To get a carbon-based qubit, we pay attention to the two-electron conduction band of a graphene quantum dot (GQD) in the presence of an external magnetic field and an extrinsic Rashba spin-orbit interaction (SOI). To help understand the formation of the two-electron spectra, we first calculate the tight-binding (TB) spectra. There exist the sensitivity of the conduction band to magnetic fields and the mixing of spin states induced by a Rashba SOI. The two factors inspire the study of the magnetic-field modulation of the conduction band for realizing a spin qubit. We present the method for calculating the electronic structure of a few-electron GQD. The roles of the Coulomb interaction and the Rashba SOI in the two-electron conduction band are investigated. The Coulomb interaction contributes to a singlet-triplet level crossing and the Rashba SOI leads to a singlet-triplet mixing. The fast initialization and coherent manipulation of spin states are demonstrated by the magnetic control of singlet-triplet splitting.

Electromagnetically induced transparency in a quantum ring: Interband transition

In this paper, we study the electromagnetically induced transparency (EIT) of a quantum ring by considering both interband and intraband transitions, under the influence of external electric and magnetic fields, as well as Rashba spin–orbit interaction (RSOI). Four band k⋅p model along with effective mass one band approximation were respectively employed to compute valence and conduction bands energy eigenvalues. We investigate the effects of applied electric and magnetic fields, as well as RSOI and the ring dimensions, on EIT. Our results reveal that the external magnetic field and the ring dimensions have a great influence on the EIT phenomenon. Ultimately, our numerical results will be used to develop devices with controllable nonlinear optical absorption and refraction.

Coherence versus quantum-memory-assisted entropic uncertainty relation of double quantum dots with Rashba spin–orbit interaction

Coherence versus quantum-memory-assisted entropic uncertainty relation of double quantum dots with Rashba spin–orbit interaction