Analysis of electron and phonon heat capacities of La2−xSrxCuO4 cuprate superconductor

Abstract

Adopting the many body quantum dynamical Green's function (GF) theory via a versatile Hamiltonian that incorporates the contribution due to harmonic electron and phonon fields and their interactions, anharmonicities and point impurities; the expressions for phononic heat capacity (PHC) and electronic heat capacity (EHC) have been obtained using the method of density of states of phonons and electrons (PDOS and EDOS). The theory is applied to the high temperature superconductor (HTS) La2−xSrxCuO4 for successful numerical estimation. The expressions of PDOS and PHC can be separated into diagonal and non-diagonal components. The non-diagonal contribution emerges only in the impure crystals and becomes extinct in pure crystals. The presence of electron-phonon (ep) coupling constant in each term of EHC is an additional and unique feature of present formulation. The results are compared with the experimental data of heat capacity for La2−xSrxCuO4 superconductor and results are found in good agreement. The electronic contribution is quite small in the comparison to the phononic contribution to total heat capacity. The doping concentration and ep coupling constant dependence of the PHC and EHC independently are investigated for La2−xSrxCuO4 crystal and observed that orderly increases with doping concentration and ep coupling constant.