Possible marginality of the superconducting gap symmetry in the oxides

It is pointed out that in systems having the electronic topology of high-T-c cuprate superconductors, isotropic s-wave electron-boson interaction in the momentum decoupling regime leads to either s or d-wave superconductivity depending on the conventional values of the Coulomb pseudopotential. Different high-T-c oxides may naturally have different gap symmetries having nevertheless the same pairing interaction and similar T(c)s. A new type of first order phase transition from s-wave to d-wave superconductivity (and vice-versa) is possible by adjusting the doping, in accordance with puzzling photoemission and Raman results where a transition from d-wave to s-wave is reported Bi2Sr2CaCu2O8 by overdoping. (C) 1998 Elsevier Science Ltd. All rights reserved.