LOW-TEMPERATURE THERMAL-EXPANSION OF SMB6 - EVIDENCE FOR A SINGLE-ENERGY SCALE IN THE THERMODYNAMICS OF KONDO INSULATORS

We have measured the thermal expansion of the Kondo insulator SmB6 from 5 to 80 K using a sensitive capacitance dilatometer. There is a pronounced negative anomaly in the linear expansion coefficient alpha, of electronic origin, which achieves a local minimum of -5 x 10(-6) K-1 at 45 K. We interpret this anomaly as a Schottky-like contribution arising from transitions across a semiconducting energy gap E(g) approximately 140 K. Although there are several energy scales in the problem, a Gruneisen analysis indicates that the thermodynamics is driven by a single energy, which we identify as the gap energy.