Rashba Spin-orbit Effect Research Articles

Effects of electron–phonon coupling and Rashba spin–orbit interaction on thermodynamic and magnetic properties of quantum dots

The thermodynamic and magnetic properties of quantum-dot structures subjected to an applied magnetic field were studied, including the longitudinal optical–phonon interaction and the Rashba spin–orbit effect. The Schrödinger equation was solved to determine the energy levels. The partition function was evaluated by summing the accessible energy levels and was then utilized to calculate the thermomagnetic functions. In this paper, we present magnetic properties by considering three interacting polarons. Our results indicated that at B=0T, the susceptibility exhibits diamagnetic behavior for all values of the Rashba spin–orbit parameter. However, the magnetic susceptibility increases with an applied magnetic field, and the system exhibits paramagnetic behavior under moderate magnetic fields. However, in situations with and without the polaron effect, the susceptibility is saturated at 0(meV/T2) under large magnetic fields. In this study, we showed that the Rashba spin–orbit interaction (SOI) strengthens the cutoff magnetic field Bc (the B value at which the magnetic nature of the dot changes from diamagnetic to paramagnetic). Rashba SOIs reduce the mean energy of the system, including polaronic interactions. Under the polaron effect, the heat capacity curve shifts to lower temperatures. A quantitative description of the magnetocaloric effect (ΔS) as a function of the Wigner and Rashba spin–orbit parameters is presented.

Twistronics of Janus transition metal dichalcogenide bilayers

Twisted multilayers of two-dimensional (2D) materials are an increasingly important platform for investigating quantum phases of matter, and in particular, strongly correlated electrons. The moir\'e pattern introduced by the relative twist between layers creates effective potentials of long wavelength, leading to electron localization. However, in contrast to the abundance of 2D materials, few twisted heterostructures have been studied until now. Here we develop a first-principles continuum theory to study the electronic bands introduced by moire patterns of twisted Janus transition metal dichalcogenide (TMD) homo- and heterobilayers. The model includes lattice relaxation, stacking-dependent effective mass, and Rashba spin-orbit coupling. We then perform a high-throughput generation and characterization of DFT-extracted continuum models for more than a hundred possible combinations of materials and stackings. Our model predicts that the moir\'e physics and emergent symmetries depend on chemical composition, vertical layer orientation, and twist angle, so that the miniband wave functions can form triangular, honeycomb, and kagome networks. Rashba spin-orbit effects, peculiar of these systems, can dominate the moir\'e bandwidth at small angles. Our work enables detailed investigation of Janus twisted heterostructures, allowing the discovery and control of novel electronic phenomena.

Experimental Evidence of t_{2g} Electron-Gas Rashba Interaction Induced by Asymmetric Orbital Hybridization.

We report the control of Rashba spin-orbit interaction by tuning asymmetric hybridization between Ti orbitals at the LaAlO_{3}/SrTiO_{3} interface. This asymmetric orbital hybridization is modulated by introducing a LaFeO_{3} layer between LaAlO_{3} and SrTiO_{3}, which alters the Ti-O lattice polarization and traps interfacial charge carriers, resulting in a large Rashba spin-orbit effect at the interface in the absence of an external bias. This observation is verified through high-resolution electron microscopy, magnetotransport and first-principles calculations. Our results open hitherto unexplored avenues of controlling Rashba interaction to design next-generation spin orbitronics.

Spin–orbit correlations and exchange-bias control in twisted Janus dichalcogenide multilayers

Janus dichalcogenide multilayers provide a paradigmatic platform to engineer electronic phenomena dominated by spin–orbit coupling. Their unique spin–orbit effects stem from the mirror symmetry breaking in each layer, which induces a colossal Rashba spin–orbit effect in comparison with the conventional dichalcogenide counterparts. Here we put forward twisted Janus dichalcogenide bilayers as a simple platform to realize spin–orbit correlated states. We demonstrate the emergence of flat bands featuring strong spin-momentum locking and the emergence of symmetry broken states with associated non-coplanar magnetization when interactions are included. We further show that the symmetry broken states can be controlled by means of a magnetic substrate, strongly impacting the non-coplanar magnetic texture of the moire unit cell. Our results put forward twisted Janus multilayers as a powerful platform to explore spin–orbit correlated physics, and highlighting the versatility of magnetic substrates to control unconventional moire magnetism.

Rashba Effect and Raman Spectra of Tl2O/PtS2 Heterostructure.

The possibility to achieve charge-to-spin conversion via Rashba spin–orbit effects provides stimulating opportunities toward the development of nanoscale spintronics. Here, we use first-principles calculations to study the electronic and spintronic properties of Tl2O/PtS2 heterostructure, for which we have confirmed the dynamical stability by its positive phonon frequencies. An unexpectedly high binding energy of −0.38 eV per unit cell depicts strong interlayer interactions between Tl2O and PtS2. Interestingly, we discover Rashba spin-splittings (with a large αR value) in the valence band of Tl2O stemming from interfacial spin–orbit effects caused by PtS2. The role of van der Waals binding on the orbital rearrangements has been studied using the electron localization function and atomic orbital projections, which explains in detail the electronic dispersion near the Fermi level. Moreover, we explain the distinct band structure alignment in momentum space but separation in real space of Tl2O/PtS2 heterostructure. Since two-dimensional (2D) Tl2O still awaits experimental confirmation, we calculate, for the first time, the Raman spectra of pristine Tl2O and the Tl2O/PtS2 heterostructure and discuss peak positions corresponding to vibrational modes of the atoms. These findings offer a promising avenue to explore spin physics for potential spintronics applications via 2D heterostructures.

Rashba spin-orbit interaction effects on thermal and magnetic properties of parabolic GaAs quantum dot in the presence of donor impurity under external electric and magnetic fields

Based on the effective mass approximation, the magnetic and thermal properties of parabolic GaAs quantum dot have been investigated in the presence of Rashba Spin-Orbit interaction (RSOI), donor impurity and applied magnetic and electric fields. The exact diagonalization method has been used to solve the Hamiltonian of an electron confined in a quantum dot (QD) and obtain the eigenenergies and the binding energy of the donor impurity as a function of various QD physical parameters. We have shown the dependence of the average statistical energy, magnetization, magnetic susceptibility and heat capacity of the donor impurity in the QD on: the Rashba interaction parameter, the magnetic and electric fields, confining frequency, and temperature. The results reveal that these parameters can tune the magnetic properties of the GaAs quantum dot and flip the sign of magnetic susceptibility from negative (diamagnetic) to positive (paramagnetic) type material.

Spin Transport under In-plane Electric Fields with Different Orientations in Undoped InGaAs/AlGaAs Multiple Quantum Wells**Supported by the National Basic Research Program of China under Grant No 2015CB921503, the National Natural Science Foundation of China under Grant Nos 61474114, 11574302, 61627822 and 11704032, and the National Key Research and Development Program of China under Grant Nos 2018YFA0209103, 2016YFB0402303 and 2016YFB0400101.

The spin-polarized photocurrent is used to study the in-plane electric field dependent spin transport in undoped InGaAs/AlGaAs multiple quantum wells. In the temperature range of 77–297 K, the spin-polarized photocurrent shows an anisotropic spin transport under different oriented in-plane electric fields. We ascribe this characteristic to two dominant mechanisms: the hot phonon effect and the Rashba spin-orbit effect which is influenced by the in-plane electric fields with different orientations. The formulas are proposed to fit our experiments, suggesting a guide of potential applications and devices.

Modification of magnetic fluctuations by interfacial interactions in artificially engineered heavy-fermion superlattices

Recent progress in the fabrication techniques of superlattices (SLs) has made it possible to sandwich several-layer-thick block layers (BLs) of heavy-fermion superconductor CeCoIn5 between conventional-metal YbCoIn5 BLs or spin-density-wave-metal CeRhIn5 BLs of a similar thickness. However, the magnetic state in each BL, particularly at the interface, is not yet understood, as experimental techniques applicable to the SL system are limited. Here, we report measurements of 59Co nuclear magnetic resonance, which is a microscopic probe of the magnetic properties inside the target BLs. In the CeCoIn5/YbCoIn5 SL, the low-temperature magnetic fluctuations of the CeCoIn5 BL are weakened as expected from the Rashba spin-orbit effect. However, in the CeCoIn5/CeRhIn5 SL, the fluctuations show an anomalous enhancement below 6 K, highlighting the importance of the magnetic proximity effect occurring near a magnetic-ordering temperature TN ~ 3 K of the CeRhIn5 BL. We suggest that the magnetic properties of the BLs can be altered by the interfacial interaction, which is an alternative route to modify the magnetic properties.

Influences of temperature and Rashba spin-orbit interaction on oscillation period of bound polaron in quantum pseudodot

In the present work, we study the influences of the temperature and the Rashba spin-orbit interaction on the oscillation period of the bound polaron in the quantum pseudodot using the Lee-Low-Pines unitary transformation, the variational method of Pekar-type and the quantum statistical theory. We have derived the oscillation period of the bound polaron in the superposition state and reported the temperature dependences and the Rashba spin-orbit interaction effects of the oscillation period of polaron when the wave vector, the electron-LO phonon coupling, the Coulomb bound potential and the chemical potential take different values.

The Rashba and Dresselhaus spin-orbit interactions effects on the optical properties of a quantum ring

Influence of Rashba and Dresselhaus spin orbit interactions (SOIs) as well as external magnetic and electric fields on optical behaviors of quantum rings (QRs) were studied. To achieve this purpose, the matrix diagonalization method was exerted to compute energy eigenvalues of the system in the presence of electric and magnetic fields. Besides, the compact density matrix approach was used to calculate the refractive index (RI) and absorption coefficient (AC) of 1 → 2, 1 → 3, 1 → 6 and 3 → 5 transitions. Moreover, by increasing the magnetic (B) and electric (F) fields, energy splitting of intersubband energy levels was increased and thus the RIs and ACs of the system are changed. The results clearly show that, position and peak value of total RIs and ACs curves of all transitions experienced significant change by increasing the magnetic and electric fields in the presence of SOIs. Finally, the effect of size variation on optical RI changes and ACs was studied. The results show that the higher inner radii, R1, is, the stronger quantum confinement and energy increase are. These results are relevant for the designing of spin-based devices.

Voltage- and Light-Controlled Spin Properties of a Two-Dimensional Hole Gas in p-Type GaAs/AlAs Resonant Tunneling Diodes

We have investigated the spin properties of a two-dimensional hole gas (2DHG) formed at the contact layer of a p-type GaAs/AlAs resonant tunneling diode (RTD). We have measured the polarized-resolved photoluminescence of the RTD as a function of bias voltage, laser intensity and external magnetic field up to 15T. By tuning the voltage and the laser intensity, we are able to change the spin-splitting from the 2DHG from almost 0 meV to 5 meV and its polarization degree from − 40% to + 50% at 15T. These results are attributed to changes of the local electric field applied to the two-dimensional gas which affects the valence band and the hole Rashba spin–orbit effect.

Transverse thermoelectric power in a semiconductor quantum well in the presence of the Rashba effect

We have studied the Rashba spin-orbit effect on a quasi-two dimensional semiconductor quantum well with a parabolic potential placed in a magnetic field parallel to the plane of the quantum well, taking into account the Zeeman coupling. The expression for the density of states and the transverse thermoelectric power of the electron gas in a quasi-two-dimensional quantum well with a parabolic potential have been obtained for the case of strong degeneracy statistics. We show that the transverse thermoelectric power depends on the strength of the spin-orbital coupling parameter, the frequency ω0, which is a characteristic parameter of the electron gas thickness, and the strength of the magnetic field.

Lande g-factor in semiconductor cylinder quantum dots under magnetic fields and spin-orbit interaction

In this paper, the electron effective Lande g-factor in semiconductor cylinder quantum dots is studied in the presence of the Rashba spin-orbit effect and an applied magnetic field parallel to the cylinder axis. For this goal, I have obtained an analytical solution to one-particle Schrodinger equation in the presence of both magnetic field and spin-orbit interaction (SOI). Then, using the obtained energy levels, I have study the electron effective Lande g-factor. It is found that: It is found that (i) energy levels strongly depend on the combined effects of external magnetic field and spin-orbit interaction strength. (ii) The effective Lande g-factor decreases when magnetic field increases. (iii) By increasing the cylinder radius ρ, the electron g-factor decreases. (iv) By increasing the strength of SOI, the electron g-factor increases.

Rashba and Dresselhaus spin-orbit couplings effects on electromagnetically induced transparency of a lens-shaped quantum dot: External electric and magnetic fields

In this article the spin of electron as well as simultaneous effects of Rashba and Dresselhaus spin-orbit interactions are considered for a lens-shaped GaAs quantum dot and the influences of applied electric field and Zeeman effect on the electromagnetically induced transparency (EIT) of this system are investigated. To do so, the absorption, refractive index as well as the group velocity of the probe light pulse are presented and discussed. Study of the absorption and refractive index reveals that, at a particular frequency of probe field, absorption diminishes, refractive index becomes unity and so the EIT occurs. Furthermore, the investigation of group velocity show that, around such frequency the probe propagation is sub-luminal, which shifts to super-luminal for higher and lower frequencies. Our results illustrate that the EIT frequency, transparency window and sub(super)-luminal frequency intervals are strongly sensitive to applied fields in the presence of spin-orbit couplings. It is found that, in comparison with the investigations with negligence of spin, the EIT behavior under the effects of applied fields are quite different.

Rashba and Dresselhaus spin-orbit interactions effects on electronic features of a two dimensional elliptic quantum dot

In this paper, electronic structure of a two dimensional elliptic quantum dot under the influence of external electric and magnetic fields are studied in the presence of Rashba and Dresselhaus spin-orbit interactions. This investigation is done computationally and to do this, at first, the effective Hamiltonian of the system by considering the spin-orbit coupling is demonstrated in the presence of applied electric and magnetic fields and afterwards the Schrödinger equation is solved using the finite difference approach. Utilizing finite element method, eigenvalues and eigenstates of the system are calculated and the effect of the external fields, the size of the dot as well as the strength of Rashba spin-orbit interaction are studied. Our results indicate that, Spin-orbit interactions, external fields and the dot size have a great influence on the electronic structure of the system.

Interference evidence for Rashba-type spin splitting on a semimetallicWTe2surface

Semimetallic tungsten ditelluride displays an extremely large nonsaturating magnetoresistance, which is thought to arise from the perfect $n\ensuremath{-}p$ charge compensation with low carrier densities in $\mathrm{WT}{\mathrm{e}}_{2}$. We find a strong Rashba spin-orbit effect in density functional calculations due to the noncentrosymmetric structure. This lifts twofold spin degeneracy of the bands. A prominent umklapp interference pattern is observed by our scanning tunneling microscopic measurements at 4.2 K, which differs distinctly from the surface atomic structure demonstrated at 77 K. The energy dependence of umklapp interference shows a strong correspondence with densities of states integrated from ARPES measurement, manifesting a fact that the bands are spin-split on the opposite sides of \ensuremath{\Gamma}. Spectroscopic survey reveals the electron/hole asymmetry changes alternately with lateral locations along the $b$ axis, providing a microscopic picture for double-carrier transport of semimetallic $\mathrm{WT}{\mathrm{e}}_{2}$. The conclusion is further supported by our ARPES results and Shubnikov--de Haas (SdH) oscillations measurements.

Spin-orbit coupling, electron transport and pairing instabilities in two-dimensional square structures

Rashba spin-orbit effects and electron correlations in the two-dimensional cylindrical lattices of square geometries are assessed using mesoscopic two-, three- and four-leg ladder structures. Here the electron transport properties are systematically calculated by including the spin-orbit coupling in tight binding and Hubbard models threaded by a magnetic flux. These results highlight important aspects of possible symmetry breaking mechanisms in square ladder geometries driven by the combined effect of a magnetic gauge field spin-orbit interaction and temperature. The observed persistent current, spin and charge polarizations in the presence of spin-orbit coupling are driven by separation of electron and hole charges and opposite spins in real-space. The modeled spin-flip processes on the pairing mechanism induced by the spin-orbit coupling in assembled nanostructures (as arrays of clusters) engineered in various two-dimensional multi-leg structures provide an ideal playground for understanding spatial charge and spin density inhomogeneities leading to electron pairing and spontaneous phase separation instabilities in unconventional superconductors. Such studies also fall under the scope of current challenging problems in superconductivity and magnetism, topological insulators and spin dependent transport associated with numerous interfaces and heterostructures.

Rashba spin–orbit effect on dwell time in graphene asymmetrical barrier

We investigated the dwell time of electrons tunneling through an asymmetric barrier in monolayer graphene with the Rashba spin–orbit interaction (RSOI). The results show that the dwell time oscillates by increasing the barrier width, RSOI strength, and the bias voltage. In addition, when an external electric field is present, the spin polarization can be observed, whereas for the RSOI alone it is zero. Furthermore, it is found that electrons with different spin orientations will spend different times through the barrier. The difference of the dwell time between spin-up and spin-down electrons arises from the Rashba spin–orbit interaction. It can be concluded that Rashba spin–orbit effect can cause a natural spin filter mechanism in the time domain.

Induced spin-accumulation and spin-polarization in a quantum-dot ring by using magnetic quantum dots and Rashba spin-orbit effect

The effect of magnetic contacts on spin-dependent electron transport and spin-accumulation in a quantum ring, which is threaded by a magnetic flux, is studied. The quantum ring is made up of four quantum dots, where two of them possess magnetic structure and other ones are subjected to the Rashba spin-orbit coupling. The magnetic quantum dots, referred to as magnetic quantum contacts, are connected to two external leads. Two different configurations of magnetic moments of the quantum contacts are considered; the parallel and the anti-parallel ones. When the magnetic moments are parallel, the degeneracy between the transmission coefficients of spin-up and spin-down electrons is lifted and the system can be adjusted to operate as a spin-filter. In addition, the accumulation of spin-up and spin-down electrons in non-magnetic quantum dots are different in the case of parallel magnetic moments. When the intra-dot Coulomb interaction is taken into account, we find that the electron interactions participate in separation between the accumulations of electrons with different spin directions in non-magnetic quantum dots. Furthermore, the spin-accumulation in non-magnetic quantum dots can be tuned in the both parallel and anti-parallel magnetic moments by adjusting the Rashba spin-orbit strength and the magnetic flux. Thus, the quantum ring with magnetic quantum contacts could be utilized to create tunable local magnetic moments which can be used in designing optimized nanodevices.

Spin-polarization and spin-dependent logic gates in a double quantum ring based on Rashba spin-orbit effect: Non-equilibrium Green's function approach

Spin-dependent electron transport in an open double quantum ring, when each ring is made up of four quantum dots and threaded by a magnetic flux, is studied. Two independent and tunable gate voltages are applied to induce Rashba spin-orbit effect in the quantum rings. Using non-equilibrium Green's function formalism, we study the effects of electron-electron interaction on spin-dependent electron transport and show that although the electron-electron interaction induces an energy gap, it has no considerable effect when the bias voltage is sufficiently high. We also show that the double quantum ring can operate as a spin-filter for both spin up and spin down electrons. The spin-polarization of transmitted electrons can be tuned from −1 (pure spin-down current) to +1 (pure spin-up current) by changing the magnetic flux and/or the gates voltage. Also, the double quantum ring can act as AND and NOR gates when the system parameters such as Rashba coefficient are properly adjusted.