¹²⁵Te NMR study of the bulk of topological insulators Bi₂Te₃ and Sb₂Te₃

The narrow band gap semiconductors Bi₂Te₃ and Sb₂Te₃ are well known for their room temperature thermoelectric performance. Recently, they were shown to serve as model systems of three-dimensional topological insulators with a bulk band gap and very robust, spin-resolved surface states due to a special band inversion in their periodic bulk. Evidently, it is of interest to investigate the special surface states with a local probe like nuclear magnetic resonance (NMR). However, especially the bulk NMR of these materials shows peculiar and rather unexpected phenomena, e. g., a magnetic field induced deformation of the local charge symmetry and excessive line broadening due to a special internuclear coupling. Here we report a comprehensive account of the room temperature NMR properties of the spin-1/2 nucleus ¹²⁵Te of single crystalline Bi₂Te₃ and Sb₂Te₃. This includes a very unusual spin-lattice relaxation that seems not to be reflected in the NMR shift, as well as an exchange enhanced NMR line broadening.