All-electrical detection of the relative strength of Rashba and Dresselhaus spin-orbit interaction in quantum wires

Magnetotransport Signatures of Superconducting Cooper Pairs Carried by Topological Surface States in Bismuth Selenide

As topological insulators (TIs) are becoming increasingly intriguing, the community is exploring transformative applications that require interfacing TIs with other materials such as ferromagnets or superconductors. Herein, we report on the manifestations of superconducting electrons carried by topological surface states (TSS) in Bi2Se3 films. As key signatures of TSS-carried Cooper pairs, we uncover the hysteresis of magnetoresistance (MR) and the switching behavior of anisotropic magnetoresistance (AMR). For in-plane fields perpendicular to the injected current, AMR shows negative switching (resistance drop) when the contacts become superconducting, which is consistent with a cooperative Zeeman effect enabled by the spin-momentum locking of TSS. The MR and AMR behaviors are robust, occurring reliably in multiple samples, from different sources, and with different defect concentrations. Our findings can guide novel developments in superconductor/TI quantum devices relying on supercurrent detection as well as lead to more refined transport signatures of Majorana zero-modes in the future.

Effective Landé factors for an electrostatically defined quantum point contact in silicene

The transconductance and effective Landé \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$g^*$$\end{document}g∗ factors for a quantum point contact defined in silicene by the electric field of a split gate is investigated. The strong spin–orbit coupling in buckled silicene reduces the \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$g^*$$\end{document}g∗ factor for in-plane magnetic field from the nominal value 2 to around 1.2 for the first- to 0.45 for the third conduction subband. However, for perpendicular magnetic field we observe an enhancement of \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$g^*$$\end{document}g∗ factors for the first subband to 5.8 in nanoribbon with zigzag and to 2.5 with armchair edge. The main contribution to the Zeeman splitting comes from the intrinsic spin–orbit coupling defined by the Kane–Mele form of interaction.

Ferroelectric control of Rashba spin orbit coupling at the GeTe(111)/InP(111) interface

GeTe is a prototypical compound of a new class of multifunctional materials, i.e., ferroelectric Rashba semiconductors (FRS). In the present work, by combining the first-principles calculations and Rashba model analysis, we reexamine Rashba spin-orbit coupling (SOC) in a GeTe(111) crystal and clarify its linear Rashba SOC strength. We further investigate Rashba SOC at the interface of a GeTe(111)/InP(111) superlattice and demonstrate the ferroelectric manipulation of Rashba SOC in detail. A large modulation of Rashba SOC is obtained, and surprisingly, we find that Rashba SOC does not monotonically increase with the increase of ferroelectric displacement, due to the parabola opening reversal of Rashba splitting bands. In addition, a reversal of the spin texture is realized by tuning the ferroelectric polarization. Our investigation provides a deep insight into the ferroelectric control of Rashba SOC, which is of great importance in FRS spin field effect transistors.

Tunneling Anomalous and Spin Hall Effects

We predict, theoretically, the existence of the anomalous Hall effect when a tunneling current flows through a tunnel junction in which only one of the electrodes is magnetic. The interfacial spin-orbit coupling present in the barrier region induces a spin-dependent momentum filtering in the directions perpendicular to the tunneling current, resulting in a skew tunneling even in the absence of impurities. This produces an anomalous Hall conductance and spin Hall currents in the nonmagnetic electrode when a bias voltage is applied across the tunneling heterojunction. If the barrier is composed of a noncentrosymmetric material, the anomalous Hall conductance and spin Hall currents become anisotropic with respect to both the magnetization and crystallographic directions, allowing us to separate this interfacial phenomenon from the bulk anomalous and spin Hall contributions. The proposed effect should be useful for proving and quantifying the interfacial spin-orbit fields in metallic and metal-semiconductor systems.

Direct determination of spin-orbit interaction coefficients and realization of the persistent spin helix symmetry

The spin-orbit interaction plays a crucial role in diverse fields of condensed matter, including the investigation of Majorana fermions, topological insulators, quantum information and spintronics. In III-V zinc-blende semiconductor heterostructures, two types of spin-orbit interaction--Rashba and Dresselhaus--act on the electron spin as effective magnetic fields with different directions. They are characterized by coefficients α and β, respectively. When α is equal to β, the so-called persistent spin helix symmetry is realized. In this condition, invariance with respect to spin rotations is achieved even in the presence of the spin-orbit interaction, implying strongly enhanced spin lifetimes for spatially periodic spin modes. Existing methods to evaluate α/β require fitting analyses that often include ambiguity in the parameters used. Here, we experimentally demonstrate a simple and fitting parameter-free technique to determine α/β and to deduce the absolute values of α and β. The method is based on the detection of the effective magnetic field direction and the strength induced by the two spin-orbit interactions. Moreover, we observe the persistent spin helix symmetry by gate tuning.

Crystallographic plane tuning of magnetoplasmon excitations in two-dimensional electron gas systems

We investigate theoretically the magnetoplasmon spectrum of two-dimensional electron gas systems grown along different crystallographic directions, which are modulated by both the Dresselhaus spin-orbit interaction (DSOI) and the Rashba spin-orbit interaction (RSOI). Because the DSOI depends on the crystallographic orientation, the magnetoplasmon spectrum in the presence of the DSOI shows distinct features for different crystallographic planes. For some high-index planes, such as (140) and (114), the magnetoplasmon spectrum is anisotropic even under the pure-DSOI modulation, which is different from the isotropic behavior for the high-symmetry (001) plane. The coexistence of the DSOI and the RSOI leads to more drastic variations of the anisotropic magnetoplasmon spectrum in different crystallographic planes, which are revealed from the splittings of the collective excitation modes and the intensity of the spin density excitation at the anticrossing center of the splittings.

Acoustically induced spin-orbit interactions revealed by two-dimensional imaging of spin transport in GaAs

Magneto-optic Kerr microscopy was employed to investigate the spin-orbit interactions of electrons traveling in semiconductor quantum wells using surface acoustic waves (SAWs). Two-dimensional images of the spin flow induced by SAWs exhibit anisotropic spin precession behaviors caused by the coexistence of different types of spin-orbit interactions. The dependence of spin-orbit effective magnetic fields on SAW intensity indicates the existence of acoustically controllable spin-orbit interactions resulting from the strain and Rashba contributions induced by the SAWs.

Spin-orbit interaction induced anisotropic property in interacting quantum wires

: We investigate theoretically the ground state and transport property of electrons in interacting quantum wires (QWs) oriented along different crystallographic directions in (001) and (110) planes in the presence of the Rashba spin-orbit interaction (RSOI) and Dresselhaus SOI (DSOI). The electron ground state can cross over different phases, e.g., spin density wave, charge density wave, singlet superconductivity, and metamagnetism, by changing the strengths of the SOIs and the crystallographic orientation of the QW. The interplay between the SOIs and Coulomb interaction leads to the anisotropic dc transport property of QW which provides us a possible way to detect the strengths of the RSOI and DSOI.PACS numbers: 73.63.Nm, 71.10.Pm, 73.23.-b, 71.70.Ej.

Large anisotropy of the spin-orbit interaction in a single InAs self-assembled quantum dot

The anisotropy of the spin-orbit interaction (SOI) is studied for a single uncapped InAs self-assembled quantum dot holding just a few electrons. The SOI energy is evaluated from anticrossing or SOI-induced hybridization between the ground and excited states with opposite spins. The magnetic angular dependence of the SOI energy falls on an absolute cosine function for azimuthal rotation, and a cosinelike function for tilting rotation. Furthermore, the SOI energy is quenched for a specific magnetic field vector. The angular dependence of SOI is found to compare well with calculation of Rashba SOI in a two-dimensional harmonic potential.

Crystallographic plane tuning of charge and spin transport in semiconductor quantum wires

We investigate theoretically the charge and spin transport in quantum wires grown along different crystallographic planes in the presence of the Rashba spin-orbit interaction (RSOI) and the Dresselhaus spin-orbit interaction (DSOI). We find that changing the crystallographic planes leads to a variation of the anisotropy of the conductance due to a different interplay between the RSOI and DSOI, since the DSOI is induced by bulk inversion asymmetry, which is determined by crystallographic plane. This interplay depends sensitively on the crystallographic planes, and consequently leads to the anisotropic charge and spin transport in quantum wires embedded in different crystallographic planes.

Gate-controlled spin-orbit interaction in a parabolic GaAs/AlGaAs quantum well

We study the tunability of the spin-orbit interaction in a two-dimensional electron gas with a front and a back gate electrode by monitoring the spin precession frequency of drifting electrons using time-resolved Kerr rotation. The Rashba spin splitting can be tuned by the gate biases, while we find a small Dresselhaus splitting that depends only weakly on the gating. We determine the absolute values and signs of the two components and show that for zero Rashba spin splitting the anisotropy of the spin-dephasing rate vanishes.