Theory of weak localization in two-dimensional high-mobility semiconductor systems is developed with allowance for the spin-orbit interaction. The obtained expressions for anomalous magnetoresistance are valid in the whole range of classically weak magnetic fields and for arbitrary strengths of bulk and structural inversion asymmetry contributions to the spin splitting. The theory serves for both diffusive and ballistic regimes of electron propagation taking into account coherent backscattering and nonbackscattering processes. The transition between weak localization and antilocalization regimes is analyzed. The manifestation of the mutual compensation of Rashba and Dresselhaus spin splittings in magnetoresistance is discussed. Perfect description of experimental data on anomalous magnetoresistance in high-mobility heterostructures is demonstrated. The in-plane magnetic field dependence of the conductivity caused by an interplay of the spin-orbit splittings and Zeeman effect is described theoretically.
Theory of weak localization is developed for two-dimensional holes in the presence of in-plane magnetic field. The Zeeman splitting even in the hole momentum results in the spin-dependent phase changing the quantum interference. The negative correction to the conductivity is shown to decrease by a factor of two by the in-plane magnetic field. The positive magnetoconductivity in a classically weak perpendicular field caused by the weak localization is calculated for both quadratic and quartic in momentum Zeeman hole splittings. Calculations show that the conductivity corrections are very close …
General framework for transport in spin-orbit-coupled superconducting heterostructures: Nonuniform spin-orbit coupling and spin-orbit-active interfaces
Van der Waals heterostructures composed of multiple few layer crystals allow the engineering of novel materials with predefined properties. As an example, coupling graphene weakly to materials with large spin orbit coupling (SOC) allows to engineer a sizeable SOC in graphene via proximity effects. The strength of the proximity effect depends on the overlap of the atomic orbitals, therefore, changing the interlayer distance via hydrostatic pressure can be utilized to enhance the interlayer coupling between the layers. In this work, we report measurements on a graphene/WSe$_2$ heterostructure ex…
We show that Ge concentration oscillations within the quantum well region of a Si/SiGe heterostructure can significantly enhance the spin-orbit coupling of the low-energy conduction-band valleys. Specifically, we find that for Ge oscillation wavelengths near $λ= 1.57~\text{nm}$ with an average Ge concentration of $\bar{n}_{\text{Ge}} = 5\%$ in the quantum well region, a Dresselhaus spin-orbit coupling is induced, at all physically relevant electric field strengths, which is over an order of magnitude larger than what is found in conventional Si/SiGe heterostructures without Ge concentration os…
Swapping Exchange and Spin-Orbit Coupling in 2D van der Waals Heterostructures
基于二维多层范德华异质结构，提出了交换和自旋轨道耦合两种最重要的自旋相互作用的概念。具体而言，我们表明，通过执行现实的从头算模拟，由双层石墨烯夹在一个2D铁磁体Cr $_2$ Ge $_2$ Te $_6$（CGT）和单层WS $_2$，是一个单一的设备，不仅能够产生，而且还交换两个相互作用。通过双层石墨烯中的栅极依赖层极化和短程自旋轨道和交换邻近效应的相互作用来实现高效交换，所述短程自旋轨道和交换邻近效应仅影响与石墨烯材料接触的层。我们称这些结构为ex-so-tic，用于通过门控在单个设备中提供交换（ex）或自旋轨道（so）耦合。这种双功能器件展示了使用2D晶体多层膜的范德华自旋电子学工程的潜力。
The effect of spin currents on the magnetic order of insulating antiferromagnets (AFMs) is of fundamental interest and can enable new applications. Toward this goal, characterizing the spin-orbit torques (SOT) associated with AFM/heavy metal (HM) interfaces is important. Here we report the full angular dependence of the harmonic Hall voltages in a predominantly easy-plane AFM, epitaxial c-axis oriented $α$-Fe$_2$O$_3$ films, with an interface to Pt. By modeling the harmonic Hall signals together with the $α$-Fe$_2$O$_3$ magnetic parameters, we determine the amplitudes of field-like and damping…
Electron-mediated ferromagnetism and small spin-orbit interaction in a molecular-beam-epitaxy grown n-type $GaAs/Al_{0.3}Ga_{0.7}As$ heterostructure with Mn $δ$-doping
Efficient Spin-Orbit Torque Switching with Non-Epitaxial Chalcogenide Heterostructures
近年来，拓扑绝缘体（TI）产生的自旋轨道矩（SOT）受到越来越多的关注。这些TI通常由外延生长的硫族化合物形成，具有极高的SOT效率，在下一代自旋电子器件中具有很大的潜力。然而，这些硫族化物的外延需要确保拓扑保护的表面态（TSS）的存在，这限制了在工业中使用这些材料的可行性。在这项工作中，我们表明，非外延的Bi $_{x}$ Te $_{1-x}$ /铁磁异质结制备的常规磁控溅射具有巨大的SOT效率，即使没有TSS。通过谐波电压测量和磁滞回线位移测量，我们发现这种非外延异质结构的体自旋轨道相互作用产生的类阻尼SOT效率在室温下可以达到大于100%的值。我们进一步证明了这些Bi $_{x}$ Te $_{1-x}$为基础的异质结构与热稳定的铁磁层，这表明，这种非外延硫族化物材料可以是潜在的有效的SOT源在未来的SOT磁存储器件的电流诱导SOT开关。
Proximity-Induced Spin-Orbit Coupling in Graphene-Bi$_{1.5}$Sb$_{0.5}$Te$_{1.7}$Se$_{1.3}$ Heterostructures
邻近耦合可以极大地增强石墨烯中微弱的本征自旋轨道耦合。在这里，我们报告的邻近诱导的自旋轨道耦合在石墨烯的六方氮化硼（hBN）转移到拓扑绝缘体Bi $_{1.5}$ Sb $_{0.5}$ Te $_{1.7}$ Se $_{1.3}$（BSTS），这是生长在hBN衬底上的气相固体合成。相位相干传输测量，揭示弱本地化，使我们能够提取的载波密度依赖的相位相干长度$l_ϕ$。虽然$l_ϕ$随着hBN/石墨烯/hBN参比样品中载流子密度的增加而增加，但由于BSTS与石墨烯的邻近偶联，其在BSTS/石墨烯中降低。后者的行为的结果从D 'yakonov-Perel型自旋散射在石墨烯与一个大的邻近诱导的自旋轨道耦合强度至少为2.5 meV。
Topological insulators have emerged as an important material class for efficient spin-charge interconversion. Most topological insulators considered to date are binary or ternary compounds, with the exception of $α$-Sn. Here we report a comprehensive characterization of the growth, magnetotransport properties, and current-induced spin-orbit torques of $α$-Sn and $β$-Sn-based ferromagnetic heterostructures. We show that $α$-Sn grown with a Bi surfactant on CdTe(001) promotes large spin-orbit torques in a ferromagnetic FeCo layer at room temperature, comparable to Pt, whereas $α$-Sn grown withou…
The orbital Hall effect provides an alternative means to the spin Hall effect to convert a charge current into a flow of angular momentum. Recently, compelling signatures of orbital Hall effects have been identified in 3d transition metals. Here, we report a systematic study of the generation, transmission, and conversion of orbital currents in heterostructures comprising 3d, 5d, and 4f metals. We show that the orbital Hall conductivity of Cr reaches giant values of the order of 5*10^5 Ohm^{-1} m^{-1} and that Pt presents a strong orbital Hall effect in addition to the spin Hall effect. Measur…
The spin-orbit interaction and spin-relaxation mechanisms of a shallow InAs quantum well heterostructure are investigated by magnetoconductance measurements as a function of an applied top-gate voltage. The data were fit using the Iordanskii--Lyanda-Geller--Pikus model and two distinct transport regimes were identified which correspond to the first and second sub-bands of the quantum well. The spin-orbit interaction splitting energy is extracted from the fits to the data, which also displays two distinct regimes. The different sub-band regimes exhibit different spin-scattering mechanisms, the …
Oxide heterostructures allow for detailed studies of 2D electronic transport phenomena. Herein, different facets of magnetotransport in selected spin-orbit-coupled systems are analyzed and characterized by their single-band and multiband behavior, respectively. Experimentally, temperature- and magnetic field-dependent measurements in the single-band system BaPbO$_3$/SrTiO$_3$ reveal strong interplay of weak antilocalization (WAL) and electron-electron interaction (EEI). Within a scheme which treats both, WAL and EEI, on an equal footing a strong contribution of EEI at low temperatures is found…
Strain and spin orbit coupling effects on electronic and optical properties of 2D CX/graphene (X = S, Se, Te) vdW heterostructure for solar energy harvesting
We investigate the proximity spin-orbit and exchange couplings in ABA and ABC trilayer graphene encapsulated within monolayers of semiconducting transition-metal dichalcogenides and the ferromagnetic semiconductor Cr$_2$Ge$_2$Te$_6$. Employing first-principles calculations we obtain the electronic structures of the multilayer stacks and extract the relevant proximity-induced orbital and spin interaction parameters by fitting the low-energy bands to model Hamiltonians. We also demonstrate the tunability of the proximity effects by a transverse electric field. Using the model Hamiltonians we als…
