NMR studies of 3D topological insulators over a large temperature range

Abstract

Results of NMR measurements of the Bi2Te3 and Bi2Se3 3D topological insulators within the temperature range 11-293 K are presented. Two lines were demonstrated in the 125Te and 77Se spectra over the whole temperature range for single crystals in the c^B0 and c||B0 orientations as well as for Bi2Te3 and Bi2Se3 powders. The observed lines correlated to two non-equivalent positions of chalcogen atoms in the crystalline structure of investigated bismuth chalcogenides. The thermal activated character of charge carriers was found for the Bi2Te3 single crystal and powder. The activation energy was evaluated. It was shown for the Bi2Se3 powder that thermally activated charge carriers did not play the main role in conductivity. The nontrivial behaviour of the 125Te and 77Se NMR spectra for Bi2Te3 and Bi2Se3 single crystals in the orientation c||B0 was found at low temperatures which could not be explained by the orientation dependence of the line shapes and shifts in the topologically trivial semiconductors without structural phase transitions.