Thermal expansion of the heavy fermion borocarbide YbNi2B2C

We have measured the thermal expansion of the heavy fermion borocarbide YbNi2B2C from room temperature to about 0.5 K using a capacitive dilatometer. The thermal expansion is anisotropic, is consistent with a crystal-field splitting on the order of 120 K, and with intermediate-valence behavior at low temperatures. The effective Gruneisen parameter is temperature dependent and we estimate its value at T = 0 to be about -7, consistent with a moderately enhanced heavy fermion state.