POSSIBLE EXPLANATION OF HIGH-T-C IN SOME 2D CUPRATE SUPERCONDUCTORS

The present paper deals with the superconducting state of a prototype of high transition temperature superconductor (SC) La1.85Sr.15CuO4 wit h strong 2D features and relatively low carrier concentration. The stu dy is carried out within the Eliashberg framework by considering a two -component total vertex consisting of electron pairing mediated by qua ntized lattice waves as well as plasmons. For the latter part the low- frequency ionic-plasmon mode has been assumed to play an important rol e in preference to electronic-plasmon in bringing about superconductiv ity. We then derive an expression for the transition temperature T-c a pplicable to layered SCs. A comparison of the calculated T-c and other properties with experiments provides support to this type of generali sed joint phonon-plasmon mechanism in LSCO. An extension of this forma lism to still higher T-c-materials, e.g. in YBCO, is encouraging. The possibility of interlayer hopping and the consequences of inclusion of non-adiabatic effects in interactions beyond Migdal's theorem are als o discussed. (C) 1997 Elsevier Science Ltd. All rights reserved.