Ferroelectricity and Large Rashba Splitting in Two-Dimensional Tellurium

Two-dimensional (2D) ferroelectric (FE) systems are promising candidates for non-volatile nanodevices. Previous studies mainly focused on 2D compounds. Though counter-intuitive, here we propose several new phases of tellurium with (anti)ferroelectricity. Two-dimensional films can be viewed as a collection of one-dimensional chains, and lone-pair instability is responsible for the (anti)ferroelectricity. The total polarization is determined to be 0.34 x 10-10 C/m for the FE ground state. Due to the local polarization field in the FE film, we show a large Rashba splitting (alpha R similar to 2 eV & sdot;angstrom) with nonzero spin Hall conductivity for experimental detection. Furthermore, a dipole-like distribution of Berry curvature is verified, which may facilitate a nonlinear Hall effect. Because Rashba-splitting/Berry-curvature distributions are fully coupled with a polarization field, they can be reversed through FE phase transition. Our results not only broaden the elemental FE materials, but also shed light on their intriguing transport phenomena.