Screened Optical-Phonon Pairing Mechanism in Electron Doped Cuprates

An effective two-dimensional dynamic interaction is developed which incorporates screening of electrons by plasmons and by optical phonons to discuss the 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 polarizabilities. Estimate of the Coulomb pseudo-potential (*=0.24), describing the screening effects on superconductivity is due to reduced electron density and large value of the optical dielectric constant as well the effective mass of electrons. The electron–phonon coupling constant () is evaluated as 1.5 which infers strong strength of coupling. Following strong coupling theory, the superconducting transition temperature of optimally doped 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 penetration depth are also estimated. The implications of the model and its analysis are discussed.