Upper critical field and isotope effect in the oxide superconductors

Abstract

In a model for which the pairing is due mainly to an electronic mechanism supplemented by a small phonon contribution, we study the isotope effect exhibited by the upper critical magnetic field He2 and compare with the critical temperature. When paramagnetic impurities are added, we find very different behaviours from that predicted in a pure phonon model The alignment of the paramagnetic spin by the external magnetic field as well as Pauli limiting is neglected in our calculations.