Disentangling bulk and surface Rashba effects in ferroelectric $α$ -GeTe

Abstract

Macroscopic ferroelectric order in $α$-GeTe with its noncentrosymmetric lattice structure leads to a giant Rashba spin splitting in the bulk bands due to strong spin-orbit interaction. Direct measure- ments of the bulk band structure using soft x-ray angle-resolved photoemission (ARPES) reveales the three-dimensional electronic structure with spindle torus shape. By combining high-resolution and spin-resolved ARPES as well as photoemission calculations, the bulk electronic structure is dis- entangled from the two-dimensional surface electronic structure by means of surface capping, which quenches the complex surface electronic structure. This unravels the bulk Rashba-split states in the ferroelectric Rashba $α$-GeTe(111) semiconductor exhibiting a giant spin-splitting with Rashba parameter $α$R around 4.2 eV/˚ A, the highest of so-far known materials.

Publication
Phys. Rev. B