La_2-xSr_xCuO₄: Low temperature specific heat and thermal conductivity

We present simultaneous measurements of the low temperature (0.04K to 1.2K) specific heat and thermal conductivity for a series of four sintered samples from the La_2-xSr_xCuO₄ system. By systematically varying the strontium (hole) concentration from x=0.05 (near-insulator) through to x=0.27 (near-metallic), we were able to study the thermal properties of the different superconducting regimes in this cuprate system. The thermal conductivity data are characterised by a weakening of the temperature dependence from T⁼³ to T⁼¹, observed in all the samples below 1K. A linear temperature variation in the specific heat data for the two most inhomogeneous superconductors (x=0.05 and 0.27) was replaced by a T^0.5 dependence for the samples with the higher transition temperatures (x=0.1 and 0.15). The specific heats of all the samples showed a large upturn (proportional to T^-2) at the lowest temperatures. The coefficients of this T^-2 term were found to have a minimum for x=0.15. We discuss these effects in terms of possible transport mechanisms.