Plasmon-phonon pairing mechanism and superconducting state parameters in layered mercury cuprates

An effective two-dimensional dynamic interaction is developed which incorpo rates screening of holes by plasmons and by optical phonons to discuss the nature of the pairing mechanism leading to superconductivity in layered mer cury cuprates. The system is treated as an ionic solid containing layers of charge carriers and a model dielectric function is set up which fulfils th e appropriate sum rules on the electronic and ionic polarizabilities. The s tatic limit of the model dielectric function is used to calculate the effec tive hole-hole coupling strength. The values of the electron-phonon couplin g strength and of the Coulomb interaction parameter indicate that the super conductor is in the strong coupling regime with effective screening of the charge carriers. The superconducting transition temperature of optimally do ped HgBa2 CuO4+delta is estimated as 120 K from Kresin's strong coupling th eory and the energy gap ratio is substantially larger than the BCS value. T he value of the isotope exponent is severely reduced below the BCS value. T he implications of the model and its analysis are discussed.