Proximity orbital and spin-orbital effects of graphene on monolayer transition-metal dichalcogenides (TMDCs) are investigated from first-principles. The Dirac band structure of graphene is found to lie within the semiconducting gap of TMDCs for sulfides and selenides, while it merges with the valence band for tellurides. In the former case, the proximity-induced staggered potential gaps and spin-orbit couplings (all on the meV scale) of the Dirac electrons are established by fitting to a phenomenological effective Hamiltonian. While graphene on MoS 2 , MoSe 2 , and WS 2 has a topologically trivial band structure, graphene on WSe 2 exhibits inverted bands. Using a realistic tight-binding model we find topologically protected helical edge states for graphene zigzag nanoribbons on WSe 2 , demonstrating the quantum spin Hall effect. This model also features "half-topological states," which are protected against time-reversal disorder on one edge only.

We investigate an effective model of proximity modified graphene (or symmetrylike materials) with broken time-reversal symmetry. We predict the appearance of quantum anomalous Hall phases by computing bulk band gap and Chern numbers for benchmark combinations of system parameters. Allowing for staggered exchange field enables quantum anomalous Hall effect in flat graphene with Chern number C = 1. We explicitly show edge states in zigzag and armchair nanoribbons and explore their localization behavior. Remarkably, the combination of staggered intrinsic spin-orbit and uniform exchange coupling gives topologically protected (unlike in time-reversal systems) pseudohelical states, whose spin is opposite in opposite zigzag edges. Rotating the magnetization from out of plane to in plane makes the system trivial, allowing to control topological phase transitions. We also propose, using density functional theory, a material platform-graphene on Ising antiferromagnet MnPSe3-to realize staggered exchange (pseudospin Zeeman) coupling.

We investigate topological properties of models that describe graphene on realistic substrates which induce proximity spin-orbit coupling in graphene. A Z_{2} phase diagram is calculated for the parameter space of (generally different) intrinsic spin-orbit coupling on the two graphene sublattices, in the presence of Rashba coupling. The most fascinating case is that of staggered intrinsic spin-orbit coupling which, despite being topologically trivial, Z_{2}=0, does exhibit edge states protected by time-reversal symmetry for zigzag ribbons as wide as micrometers. We call these states pseudohelical as their helicity is locked to the sublattice. The spin character and robustness of the pseudohelical modes is best exhibited on a finite flake, which shows that the edge states have zero g factor, carry a pure spin current in the cross section of the flake, and exhibit spin-flip reflectionless tunneling at the armchair edges.

Andreev reflection spectroscopy of ferromagnet-superconductor (FS) junctions is an important probe of spin polarization. We theoretically investigate spin-polarized transport in FS junctions in the presence of Rashba and Dresselhaus interfacial spin-orbit fields and show that Andreev reflection can be controlled by changing the magnetization orientation. We predict a giant in-and out-of-plane magnetoanisotropy of the junction conductance. If the ferromagnet is highly spin polarized-in the half-metal limit-the magnetoanisotropic Andreev reflection depends universally on the spin-orbit fields only. Our results show that Andreev reflection spectroscopy can be used for sensitive probing of interfacial spin-orbit fields in a FS junction. DOI: 10.1103/PhysRevLett.115.116601 PACS numbers: 72.25.-b, 74.25.F-, 75.47.-m, 85.75.-d Spin-orbit coupling (SOC) is a key interaction in spintronics [1][2][3], allowing an electrical control of magnetization and, vice versa, a magnetic control of electrical current. In systems lacking space inversion symmetry-be it bulk, hybrid structures, junctions-SOC induces spinorbit fields [1,2] as an emergent phenomenon. We are in particular concerned here with interfacial spin-orbit fields which are believed to be behind a wealth of new phenomena, not existent or fragile in the bulk, such as the tunneling anisotropic magnetoresistance (TAMR) [4][5][6][7], interfacial spin-orbit torques [8], or Skyrmions [9].Interfacial spin-orbit fields are also important in semiconductor-superconductor [10-13] and ferromagnetsuperconductor (FS) junctions [14] for creating Majorana quasiparticle states. It is the latter junctions that we focus on. We investigate the interplay of magnetism and spin-orbit fields. We show that this interplay leads to marked anisotropies in the junction conductance with respect to the orientation of magnetization. The most robust is the outof-plane anisotropy (plane being the interface), which arises from the omnipresent Rashba field [15]. A more subtle is the in-plane anisotropy, which arises from the interference between the Rashba and Dresselhaus [16] fields, induced by a twofold anisotropy of the C 2v type. A zinc-blende semiconductor (say, GaAs or InAs) as a barrier in an FS junction would create such an anisotropy, generating spin-orbit fields C 2v "butterfly" patterns, as shown by first-principles calculations [17]. Remarkably, the resulting magnetoconductance anisotropy-we term it magnetoanisotropic Andreev reflection (MAAR)-is giant in comparison to TAMR, its normal-state counterpart, reaching a universal behavior in the half-metallic case. This is because Andreev reflection (AR) (which has no counterpart in the normal-state TAMR) is strongly influenced by interfacial spin-orbit fields.We specifically examine the influence of SOC and crystalline anisotropy on the process of AR in which the reflected particle carries the information about both the phase of the incident particle and the macroscopic phase of the superconductor to which a Cooper pair is being transferre...

Spin-orbit coupling (SOC) is a key interaction in spintronics, allowing an electrical control of spin or magnetization and, vice versa, a magnetic control of electrical current. However, recent advances have revealed much broader implications of SOC that is also central to the design of topological states, including topological insulators, skyrmions, and Majorana fermions, or to overcome the exclusion of two-dimensional ferro-magnetism expected from the Mermin-Wagner theorem. SOC and the resulting emergent interfacial spin-orbit fields are simply realized in junctions through structural inversion asymmetry, while the anisotropy in magnetoresistance (MR) allows for their experimental detection. Surprisingly, we demonstrate that an all-epitaxial ferromagnet/ MgO/metal junction with only a negligible MR anisotropy undergoes a remarkable transformation below the superconducting transition temperature of the metal. The superconducting junction has a three orders of magnitude higher MR anisotropy and supports the formation of spin-triplet superconductivity, crucial for superconducting spintronics, and topologically-protected quantum computing. Our findings call for revisiting the role of SOC in other systems which, even when it seems negligible in the normal state, could have a profound influence on the superconducting response.For over 150 years magnetoresistive effects have provided attractive platforms to study spin-dependent phenomena and enable key spintronic applications [1]. Primarily, spintronics relies on junctions with at least two ferromagnetic layers to provide sufficiently large magnetoresistance (MR). Record room-temperature MR and commercial applications employ junctions of common ferromagnets, such as Co and Fe with MgO tunnel barrier [2,3]. Alternatively, MR occurs in single ferromagnetic layers with an interplay of interfacial spin-orbit coupling (SOC). However, in metallic systems this phenomenon, known as the tunneling anisotropic MR (TAMR) [4], is typically < 1% and precludes practical applications. Here we show experimentally that a negligible MR in an all-epitaxial ferromagnet/MgO/metal junction is drastically enhanced below the superconducting transition temperature of the metal. We explain this peculiar behavior with the role of the interfacial SOC in the formation of spin-triplet superconductivity which can enable low-power superconducting spintronics [5-7] and topologically-protected quantum computing [8,9].

We study theoretically the effects of interfacial Rashba and Dresselhaus spin-orbit coupling in superconductor/ferromagnet/superconductor (S/F/S) Josephson junctions-with allowing for tunneling barriers between the ferromagnetic and superconducting layers-by solving the Bogoljubov-de Gennes equation for realistic heterostructures and applying the Furusaki-Tsukada technique to calculate the electric current at a finite temperature. The presence of spin-orbit couplings leads to out-of-plane and in-plane magnetoanisotropies of the Josephson current, which are giant in comparison to current magnetoanisotropies in similar normal-state ferromagnet/normal metal (F/N) junctions. Especially huge anisotropies appear in the vicinity of 0-π transitions, caused by the exchange-split bands in the ferromagnetic metal layer. We also show that the direction of the Josephson critical current can be controlled (inducing 0-π transitions) by the strength of the spin-orbit coupling and, more crucial, by the orientation of the magnetization. Such a control can bring new functionalities into Josephson junction devices.

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We show electric field control of the spin accumulation at the interface of the oxide semiconductor Nb-SrTiO_{3} with Co/AlO_{x} spin injection contacts at room temperature. The in-plane spin lifetime τ_{∥}, as well as the ratio of the out-of-plane to in-plane spin lifetime τ_{⊥}/τ_{∥}, is manipulated by the built-in electric field at the semiconductor surface, without any additional gate contact. The origin of this manipulation is attributed to Rashba spin orbit fields (SOFs) at the Nb-SrTiO_{3} surface and shown to be consistent with theoretical model calculations based on SOF spin flip scattering. Additionally, the junction can be set in a high or low resistance state, leading to a nonvolatile control of τ_{⊥}/τ_{∥}, consistent with the manipulation of the Rashba SOF strength. Such room temperature electric field control over the spin state is essential for developing energy-efficient spintronic devices and shows promise for complex oxide based (spin) electronics.