ROLE OF LONG – RANGE ELECTRON - PHONON AND COULOMB INTERACTIONS IN HIGH - TCCUPRATE SUPERCONDUCTORS

Abstract

The effect of electron – phonon and Coulomb interactions between charge carriers on the properties ofcuprate superconductors, has been studied. The expectation value of the Hamiltonian was evaluated using second quantization and many body techniques. The equation for the energy of the system at ground state was obtained from the product of the expectation value and the thermal activation factor, exp (-E1/kT). Values of specific heat and entropy against absolute temperature were calculated. In these calculations, the onsite energy of oxygen (Ep) was fixed at 2.0 x 10-6eV. The onsite energy of copper (Ed), hybridization energy of oxygen and copper bands (tpd), the electron – phonon interaction energy, (gep) and energy due to repulsion of copper holes occupying the same orbital (ud), were varied. From the results, it was found that increase in the values of parameters Ed, tpd, gep and ud leads to increase in the transition temperature. It was further found that entropy and specific heat decrease with increase in the values of the parameters. It is concluded that long range electron – phonon and local Coulomb interactions increase the transition temperature of superconducting cuprates. We have obtained a transition temperature of 60 K for some parameters,which correspond to the 60 K plateau ofYBaCuO oxygen content at x = 6.7