NMR relaxation in the topological Kondo insulator SmB6

作者：Schlottmann P^*

来源：Physical Review B, 2014, 90(16): 165127.

DOI：10.1103/PhysRevB.90.165127

SmB6 has been predicted to be a strong topological Kondo insulator, and experimentally it has been confirmed that at low temperatures the electrical conductivity only takes place at the surfaces of the crystal. We study the temperature and magnetic field dependence of the NMR Knight shift and relaxation rate arising from the topological conduction states. For the clean surface the Landau quantization of the surface states gives rise to highly degenerate discrete levels for which the Knight shift is proportional to the magnetic field B and inversely proportional to the temperature T. The relaxation rate 1/T-1 is not Korringa-like. For the more realistic case of a surface with a low concentration of defects (dirty limit) the scattering of the electrons leads to a broadening of the Landau levels and hence to a finite density of states. The mildly dirty surface case leads to a T-independent Knight shift proportional to B and a Korringa-like 1/T-1 at low T. The wave functions of the surface states are expected to fall off exponentially with distance from the surface giving rise to a superposition of relaxation times, i.e., a stretched exponential. It is questionable that the experimental B-11 Knight shift and relaxation rate arise from the surface states of the TKI. An alternative explanation is that the bulk susceptibility and the B-11 NMR properties are the consequence of the in-gap bulk states originating from magnetic exciton bound states proposed by Riseborough [Phys. Rev. B 68, 235213 (2003)].

• 出版日期2014-10-21