Evolution to an anisotropic band structure caused by Sn doping in Bi_1.995Sn_0.005Te₃ single crystals

Abstract

Magnetotransport studies have established the existence of exotic electronic properties in materials of technological and fundamental interest. However, measurements of the Shubnikov–de Haas oscillations, intended to reveal information about Fermi surfaces (FSs), have mostly been carried out in magnetic fields perpendicular to the applied currents. Here, using magnetic fields not only perpendicular but also parallel to the applied currents in a given contact configuration, we investigated the anisotropic magnetotransport and the anisotropic FS properties of Bi2−x Sn x Te3 (0 ⩽ x ⩽ 0.0075) and Bi2Se3. While the magnetotransport properties of Bi2Te3 and Bi2Se3 were nearly isotropic, Bi1.995Sn0.005Te3 exhibited quite anisotropic features. These observations are attributed to the nonparabolicity of the associated bands, which evolved to more anisotropic band structures with Sn concentration. This sensitivity of the band anisotropy was rather unexpected because only a small number of dopants are known to increase disorder levels in the degenerate region. Our approach, using two different magnetic field directions in the measurements of the Shubnikov–de Haas oscillations, is a simple and easily adoptable method for shedding more light on the FSs of functional materials.