Undulated 2D materials as a platform for large Rashba spin-splitting and persistent spin-helix states

TL;DR

This paper presents a novel approach to enhance Rashba spin-orbit coupling in 2D materials through undulations, enabling large spin-splitting and small spin-precession lengths for advanced spintronics applications.

Contribution

It introduces a design principle using specific undulations in 2D materials to achieve and enhance large Rashba SOC and persistent spin-helix states.

Findings

Achieved high spin-splitting of ~0.16 eV in bent 2D MoTe2

Demonstrated that curvature-induced hybridization enhances Rashba SOC

Showed that undulations can produce large unidirectional Rashba SOC despite net-zero curvature

Abstract

Materials with large unidirectional Rashba spin-orbit coupling (SOC), resulting in persistent-spin helix states with small spin-precession length, are critical for advancing spintronics. We demonstrate a design principle achieving it through specific undulations of 2D materials. Analytical model and first-principles calculations reveal that bending-induced asymmetric hybridization brings about and even enhances Rashba SOC. Its strength $\alpha_R \propto \kappa$ (curvature) and shifting electronic levels $\Delta \propto \kappa^2$. Despite the vanishing integral curvature of typical topographies, implying a net-zero Rashba effect, our two-band analysis and electronic structure calculation of a bent 2D MoTe$_2$ show that only an interplay of $\alpha_R$ and $\Delta$ modulations results in large unidirectional Rashba SOC with well-isolated states. Their high spin-splitting $\sim 0.16$ eV, and attractively small spin-precession length $\sim 1$ nm, are among the best known. Our work uncovers major physical effects of undulations on Rashba SOC in 2D materials, opening new avenues for using their topographical deformation for spintronics and quantum computing.