Theory of magnetotransport in Bismuth (111) thin films

The surface states of Bismuth thin films have attracted much attention due to the large Rashba splitting and emergence of topological phase in the ultrathin limit. To gain a deeper understanding of the roles of surface/edge states in spin and charge transport in Bi thin films, we theoretically investigate the magnetotransport based on a sp3 tight-binding model for atomic bilayers stacked along the (111) direction, whereby the Rasbha spin-orbit coupling is captured by introducing a potential gradient in the surface bilayer. As compared to the simple Rashba two-band model, the tight-binding model is more realistic, allowing us to capture a hexagonally-warped electron pocket around the Gamma point – with spin-momentum-locking – as well as six spin-polarized hole pockets surrounding it. Applying an in-plane magnetic field can effectively shift – and distort -- these electron and hole pockets, which conspires with the suppression of back scatterings to give rise to unique magnetotransport effects (such as large anisotropic magnetoresistance and negative magnetoresistance). Comparison between theoretical and experimental results will be presented.