using nuclear magnetic resonance

The investigations of 3-dimensional topological insulators such as Bi₂Se₃ focus chiefly on the gapless surface states that emerge as a consequence of the special energy band inversion near the Fermi level induced by spin-orbit coupling. Not as much studied are the real-space effects in the bulk. The band inversion, for example, changes the wave function of the free carriers, compared to the topologically trivial counterpart. We will show that nuclear magnetic resonance (NMR) as a local, bulk probe can detect this band inversion through the electric quadrupole interaction that, in addition, measures the concentration of free carriers, e.g. originating from self-doping effects. NMR data in external fields up to 17 T, i.e., shifts, linewidths and quadrupole splittings, in doped single crystalline samples of Bi₂Se₃ are discussed.