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 fro m 5 to 80 K using a sensitive capacitance dilatometer. There is a pron ounced negative anomaly in the linear expansion coefficient alpha, of electronic origin, which achieves a local minimum of -5 x 10(-6) K-1 a t 45 K. We interpret this anomaly as a Schottky-like contribution aris ing from transitions across a semiconducting energy gap E(g) approxima tely 140 K. Although there are several energy scales in the problem, a Gruneisen analysis indicates that the thermodynamics is driven by a s ingle energy, which we identify as the gap energy.