β-detected NMR of 8Li+ in Bi, Sb, and the topological insulator Bi0.9Sb0.1

Abstract

We report the NMR Knight shift and spin-lattice relaxation of 8Li+ implanted ∼100 nm into single crystals of semimetallic Sb, Bi, and topologically insulating Bi0.9Sb0.1. We find small negative shifts (of order 100 ppm) in all three. In the insulator, the shift is nearly temperature independent, while in Bi and Sb it becomes more negative at low temperature without following the bulk susceptibility, suggesting two distinct temperature dependent contributions, possibly from the orbital and spin response. However, a simple model is unable to account for the observed shift. The spin-lattice relaxation differs in both scale and temperature dependence in all three. It is Korringa-like in Bi and remarkably is fastest in the insulating alloy and slowest in Sb with the highest bulk carrier density. These surprising results call for detailed calculations, but phenomenologically demonstrate that β-detected NMR of implanted 8Li+ is sensitive to the magnetic response of low-density carriers. The prospects for depth-resolved studies of conventional and topological surface states at lower implantation energies are good.