PARAMAGNETIC-RESONANCE STUDY OF THE HIGH-TEMPERATURE SUPERCONDUCTOR YBA2CU3O7-DELTA AND THE GAP EQUATION

In this Letter, we report an electron-paramagnetic resonance study of Cu**2** plus in a YBa//2Cu//3O//7// minus // delta ( delta congruent 0. 1) polycrystalline sample and make an effort to understand the high-temperature superconductivity. We investigate the potential between Cu**2** plus -O**2** minus -Cu**2** plus atoms and obtain a numerical solution of the BCS gap equation which shows higher T//c than the analytical form given by the BCS theory for certain values of N(0)V, where N(0) is the density of states near the Fermi surface and V is the coupling constant of the electron-phonon interaction.