Low-temperature specific heat of Sr₂RuO₄

We report low-temperature measurements 0.07 K ≤ T ≤ 2 K of the specific heat, C, of the perovskite superconductor Sr₂RuO₄. Based on a detailed analysis of our data with respect to both sample quality (as measured by T_c = 0.43 K - 1.17 K) and magnetic-field dependence, it is shown that the electronic contribution to the specific heat, which contains the desired information on the gap structure, is superimposed by at least two additional contributions: a Schottky-type hump at T ≈ 0.1 - 0.2 K and a low-temperature upturn in C/T at T < 0.1 K. We discuss possible origins of these additional contributions and their implications for the interpretation of low-temperature C(T) data.