Screened optical-phonon pairing mechanism in electron doped cuprates

An effective two-dimensional dynamic interaction is developed which incorpo rates screening of electrons by plasmas and by optical phonons to discuss t he nature of the pairing mechanism leading to superconductivity in layered electron doped cuprates. The system is treated as an ionic solid containing layers of electrons as carriers and a model dielectric function is set up which fulfils the appropriate sum rules on the electronic and ionic polariz abilities. Estimate of the Coulomb pseudo-potential (mu* = 0.24), describin g the screening effects on superconductivity is due to reduced electron den sity and large value of the optical dielectric constant as well the effecti ve mass of electrons. The electron-phonon coupling constant (lambda) is eva luated as 1.5 which infers strong strength of coupling. Following strong co upling theory, the superconductivity transition temperature of optimally do ped Nd-Ce-CuO is estimated as 30 K and the energy gap ratio is larger than the BCS value. The isotope exponent, coherence length and magnetic penetrat ion depth are also estimated. The implications of the model and its analysi s are discussed.