Tuning Rashba effect, band inversion, and spin-charge conversion of Janus XSn2Y monolayers via an external field

We predict, through first-principles calculations, a different class of Janus two-dimensional (2D) materials XSn2Y (X, Y = P, As, Sb, and Bi; X not equal Y). It has found that these 2D monolayers have intrinsic polarization effect owing to presence of mirror-symmetry breaking. SbSn2Bi, AsSn2Sb, and PSn2As have a semiconducting feature, however AsSn2Bi, PSn2Bi, and PSn2Sb have a metallic feature with inverted band structure. When the spin-orbit coupling (SOC) is considered, the double Rashba effects are found in SbSn2Bi. Band inversion coupling with SOC leads to unexpected spin-valley splitting characteristics in AsSn2Bi, PSn2Bi, and PSn2Sb, showing a circle-type Berry curvature. The electronic and spin properties of Janus XSn2Y monolayers are tunable via applying external strain and electric field, resulting in Rashba-type spin-splitting, p(z)/p(xy) band inversion, and a Dirac cone. In particular, the sombrero band dispersion and Van Hove singularity are revealed in PSn2As by exerting tensile strain. We therefore investigate the Lifshitz transition and inverse Edelstein effect (also referred as spin-charge conversion) of the strained PSn2As. On the basis of the k.p model in the clean limit, the Drude coefficient for spin-charge conversion is estimated to be about 0.086 e/angstrom as tensile strain of +3%. Finally, the synergic effect of tensile strain and electric field is considered to manipulate the spin-charge conversion. Our results provide a class of 2D materials to investigate the Rashba effect, Lifshitz transition, and spin-charge conversion.