The phonon and electron heat capacities of cuprate superconductors

Expressions for renormalized phonon density of states (RPDOS), renormalized electron density of states (REDOS), phonon heat capacity (PHC) and electronic heat capacity (EHC) have been derived based on quantum dynamical many body double time thermodynamic Green's function (GF) theory of phonons and electrons using the effects of phonons, electrons, point impurities and anharmonicities. The theory thus developed is applied to the representative high temperature superconductor (HTS) YBa2Cu3O7−δ through numerical computation. It is found that the PHC can be resolved into diagonal and non-diagonal contributions, which are significantly influenced by defects and anharmonicities. The EHC contribution is much smaller than that of PHC. A successful agreement between theory and experiment has been observed for YBa2Cu3O7−δ. The presence of electron-phonon coupling constant in each term of EHC is an additional and new feature of the theory.