Current-induced spin-orbit torque on the surface of a transition metal dichalcogenide connected to a two-dimensional ferromagnet CrI$_3$: Effects of twisting and gating

TL;DR

This study explores how twisting and gating influence current-induced spin-orbit torque in TMDC/CrI3 bilayers, revealing significant tunability and sign reversal of the torque through these external controls.

Contribution

It demonstrates the effects of twisting and gating on SOT in TMDC/CrI3 bilayers, highlighting the potential for tunable spintronic devices beyond linear response.

Findings

Damping-like torque is greatly enhanced in n-doped MoSe2.

Twist angle can reverse the sign of the SOT.

Gate electric field significantly modulates the SOT magnitude.

Abstract

Motivated by recent progress in employing two key classes of two-dimensional materials-topological insulators and transition-metal dichalcogenides (TMDCs)-as spin sources for generating spin-orbit torque (SOT), we investigate current-induced spin polarization and the resulting SOT in bilayers composed of a TMDC (WSe$_2$ or MoSe$_2$) and ferromagnetic chromium iodide (CrI$_3$), beyond the linear response regime. Using the steady-state Boltzmann equation, we find that intra-band transitions yield a strong field-like torque on the CrI$_3$ layer, while inter-band transitions give rise to a comparatively weaker damping-like torque in the WSe$_2$/CrI$_3$ system. Remarkably, the damping-like component is enhanced by up to three orders of magnitude in n-doped MoSe$_2$, reaching a strength comparable to the field-like torque, which itself is an order of magnitude larger than that in the WSe$_2$-based bilayer. Both torque components exhibit strong asymmetry between n-type and p-type doping in WSe$_2$ and MoSe$_2$ systems. Furthermore, we demonstrate that the twist angle plays a crucial role: depending on the TMDC and chemical potential, twisting can reverse the sign of the SOT and significantly modulate its magnitude. Finally, we show that a transverse gate electric field enables substantial tunability of the SOT, by nearly one order of magnitude, and induces a sign reversal at a twist angle of $10.16^{\circ}$.