PROXIMITY INDUCED SPIN CURRENTS AND SPIN-ORBIT TORQUES IN GRAPHENE ON 1T-TAS2

Charge-spin interconversion provides a unique way to generate spin current and spin-orbit torque, which are essential for the development of spintronic devices [1]. The proximity of a transition-metal dichalcogenide (TMD) to graphene can have a profound effect on the magnetism and spin texture of graphene. This effect comes from the induced spin-orbit coupling (SOC) of the TMD, which complements the high-quality charge and spin transport of graphene [2, 3]. One of the most promising materials for SOT research is 1T-TaS₂ which comprises both strong SOC and spontaneous in-plane magnetization. When a layer of graphene is placed on top of 1T-TaS₂, a SOC and exchange interaction is proximitized to graphene electronic structure. This enables generation of spin-orbit torques (SOT) [4] without a need of spin-polarized current injection by a ferromagnet.
Using an effective tight-binding model [5] combined with quantum transport calculations, we show that the flow of an unpolarized current across a single layer of graphene proximitized with 1T-TaS₂ will exhibit SOT driven by the unpolarized injected charge current. Our results show an overall spin accumulation for the spin component perpendicular to the plane. Remarkably, the sign of the accumulated spin density depends on the electron or hole nature of the injected current. On the other hand, for the injected electrons with spins along the longitudinal direction, a spin separation is observed perpendicular to the current direction, which is the signature of the spin Hall effect. Interestingly, these results are independent of stacking type.  The subsequent interaction of the current-induced spins with the 1T-TaS₂ layer generates SOT. Our findings shed new light on the fundamental behavior of spin currents and SOT in graphene-TaS₂ heterostructures and highlight the potential of these materials for developing spintronic devices.