Angular-resolved photoemission electron spectroscopy and transport studies of the elemental topological insulator α -Sn

Gray tin, also known as α-Sn, can be turned into a three-dimensional topological insulator (3D-TI) by strain and finite-size effects. Such room-temperature 3D-TI is peculiarly interesting for spintronics due to the spin-momentum locking along the Dirac cone (linear dispersion) of the surface states. Angle-resolved photoemission spectroscopy (ARPES) has been used to investigate the dispersion close to the Fermi level in thin (001)-oriented epitaxially strained films of α-Sn for different film thicknesses as well as for different capping layers (Al, AlOx, and MgO). Indeed a proper capping layer is necessary to be able to use α-Sn surface states for spintronic applications. In contrast with free surfaces or surfaces coated with Ag, coating the α-Sn surface with Al or AlOx leads to a drop in the Fermi level below the Dirac point, and an important consequence for electronic transport is the presence of bulk states at the Fermi level. α-Sn films coated by AlOx are studied by electrical magnetotransport: Despite magnetotransport properties of the bulk electronic states of the Γ8 band playing an important role as suggested by ab initio calculations, there is clear evidence of surface states revealed by Shubnikov-de Haas oscillations corresponding to the ARPES observation.