Nuclear Magnetic Resonance Studies of Field Effects on Single Crystal SmB6

SmB6 has a cubic CsCl structure consisting of Boron octahedra at the corners of the cubic structure at the Cl sites and Samarium sitting at the body center at the Cs site. Extensive measurements were carried out on high quality single crystal SmB6 to include magnetization, resistivity, and nuclear magnetic resonance (NMR) measurements over temperature ranges between 1.6–300K and in magnetic fields up to 37T. These have revealed that SmB6 is a highly correlated gapped semiconductor, frequently referred to as a Kondo insulator. The results of 11B NMR measurements at different applied magnetic fields shows the isotropic component of the Knight shift is temperature dependent that correlates with the magnetic susceptibility, while the anisotropic component shows a much smaller temperature dependence. The low temperature anomaly in susceptibility also shows that the moment still exists at low temperatures. The temperature and field dependence of the 11B spin-lattice relaxation rate T1-1(T,H) is indicative of inter-gap states below 15K that is either suppressed or have a shifted temperature dependence with increasing magnetic field. Different theoretical models have been postulated to explain the inter-gap state responsible for the low temperature anomalies as seen in the susceptibility, Knight shift and relaxation data. The low temperature anomalies with field have been ascribed to the closing of the coherence gap.