Ionic and electronic properties of the topological insulator Bi_2Te_2Se investigated via β-detected nuclear magnetic relaxation and resonance of ~8Li

摘要

We report measurements on the high-temperature ionic and low-temperature electronic properties of the three-dimensional topological insulator Bi2Te2Se using ion-implanted Li-8 beta-detected nuclear magnetic relaxation and resonance. With implantation energies in the range 5-28 keV, the probes penetrate beyond the expected range of the topological surface state, but are still within 250 nm of the surface. At temperatures above similar to 150 K, spin-lattice relaxation measurements reveal isolated Li-8(+) diffusion with an activation energy E-A = 0.185( 8) eV and attempt frequency tau(-1)(0) = 8 +/- 3 x 10(11) s(-1) for atomic site-to-site hopping. At lower temperature, we find a linear Korringa-type relaxation mechanism with a field-dependent slope and intercept, which is accompanied by an anomalous field dependence to the resonance shift. We suggest that these may be related to a strong contribution from orbital currents or the magnetic freeze-out of charge carriers in this heavily compensated semiconductor, but that conventional theories are unable to account for the extent of the field dependence. Conventional NMR of the stable host nuclei may help elucidate their origin.