NMR Study of a Valence Fluctuating Compound SmB6

Abstract

The ¹¹ B NMR in a typical valence fluctuating compound SmB ₆ has been investigated in the temperature range between 2.5 and 850 K by the pulsed NMR technique. An unusual temperature dependence was observed in the nuclear spin-lattice relaxation rate (1/ T ₁ ). 1/ T ₁ increases rapidly with increasing temperature above about 20 K, but it remains almost constant above room temperature. This behavior is qualitatively explained by assuming a simple model density of 4f states with a gap of 50 K at the Fermi level and a band width of 500 K. Contrary to the case of usual semiconductors, the experimental result shows that another relaxation process sets in that gives a temperature independent relaxation rate below 6 K. Although the physical mechanism of this process has not been made clear yet, it is proposed that it may be due to the formation of charge localized states which are related to the conductivity at low temperatures.