Switching Rashba spin-splitting by reversing electric-field direction

The manipulation of the Rashba spin-splitting is crucial for the development of nanospintronic technology. Here, it is proposed that the Rashba spin-splitting can be turned on and off by reversing electric-field direction. By the first-principles calculations, our proposal is illustrated by a concrete example of Janus monolayer RbKNaBi. The designed RbKNaBi possesses dynamical, thermal, and mechanical stabilities, and is a large-gap quantum spin Hall insulator (QSHI) with Rashba spin-splitting near the Fermi level. A small built-in electric field is predicted due to very small electronegativity difference between the bottom and top atoms, which is very key to switch Rashba spin-splitting through the experimentally available electric field intensity. Due to out-of-plane structural asymmetry, the Janus monolayer has distinctive behaviors by applying external electric field $E$ with the same magnitude but different directions ($z$ or $\ensuremath{-}z$). Our results reveal that the Rashba energy (${E}_{R}$) and Rashba constant (${\ensuremath{\alpha}}_{R}$) are increased by the positive $E$, while a negative $E$ suppresses the Rashba splitting to disappear, and then appears again. In a certain $E$ region (0.15 $\mathrm{V}/\AA{}$ to 0.25 $\mathrm{V}/\AA{}$), switching Rashba spin-splitting can be achieved by only reversing electric-field direction. Besides, the piezoelectric strain coefficients ${d}_{11}$ and ${d}_{31}$ (5.52 pm/V and --0.41 pm/V) are predicted, which are higher than or compared with those of many 2D materials. By piezoelectric effect, the strain can also be used to tune Rashba spin-splitting of RbKNaBi. In Janus RbKNaBi monolayer, the combination of piezoelectricity and Rashba spin-splitting with topological insulating phase can promote the integration of various physical phenomena. Moreover, a possible spintronic device is proposed to realize the function of spintronic switch. Our proposed manipulation of the Rashba spin-splitting may make a special contribution to semiconductor spintronics.