PHONON RENORMALIZATION, SPECIFIC-HEAT ANOMALY AND WHY SOME ASPECTS OF MEAN-FIELD THEORY CAN BE RELEVANT FOR HIGH-TC SUPERCONDUCTIVITY

Phonon anomalies due to superconductivity in YBa2Cu3O7are correlated with the superconducting order parameter. The phonon part of the excess specific heat follows the same temperature evolution as the measured macroscopic excess heat capacity. The electronic part of the transformation entropy corresponds to about 10% of the total carrier concentration. No excess entropy was found at temperatures well above Tc. The effect of phonon contributions to the stabilization energy of the superconducting phase is discussed. © 1991 Taylor & Francis Group, LLC.