Switchable Rashba effect by dipole moment switching in an Ag2Te monolayer

Abstract

Because of the surface depolarization field, there is a critical thickness for ferroelectricity in ultrathin ferroelectric films, hindering miniaturization of high-density nonvolatile memory storage devices. A controllable Rashba effect by external electric field via switchable dipole moment could be a promising way to control and manipulate the spin degrees of freedom in spintronics. Here, based on first principles calculations, we show that non-planar Ag2Te monolayer, which has been recently predicted to be a topological insulator, possess a switchable out-of-plane electric dipole moment. The switching of the dipole can be realized by the penetration of Te atoms through the hexagonal Ag-plane. Additionally, non-planar Ag2Te shows a giant Rashba spin-splitting (alpha(R) = 3.84 eV angstrom) due to the out-of-plane electric dipole moment. Our tight binding model indicates that the origin of such large ail is the large inversion symmetry breaking term (gamma similar to 0.13 eV), which is one order of magnitude larger in non-planar Ag2Te monolayer compared with other Rashba materials. Interestingly, the Rashba effect can be turned on/off by the phase transition from non-planar to planar structure via Te displacement. Moreover, the spin-texture can be completely reversed because of switchable electric dipole moment. Our work shows a new way to realize ferroelectric-like dipole moment switching and consequently switchable Rashba spin-splitting, which may facilitate a nonvolatile electrical control of the spin degrees of freedom, down to the monolayer thickness, promising potential applications to electrically controlled spintronic devices.