EVIDENCE ON THE NATURE OF SUPERCONDUCTIVITY IN LA1.85BA0.15CUO4 FROM SPECIFIC-HEAT MEASUREMENTS

Information on the nature of the superconducting state in La//1//. //8//5Ba//0//. //1//5CuO//4 has been obtained from high-precision differential specific heat measurements on superconducting La//1//. //8//5Ba//0//. //1//5 CuO//4, and non-superconducting La//2CuO//4 and La//1//. //8//5Ba//0//. //1//5Cu//0//. //9Ni//0//. //1O//4 samples between 1. 5 and 300 K. Phonon spectra are determined that are in agreement with theoretical predictions, and evidence is obtained for strong high-temperature anharmonicity. A striking anomaly at 58 K in the specific heat of the superconducting compound may indicate a soft phonon mode.