Oxygen deficiency dependence of transition temperature in (Sm, Er) Ba₂Cu₃O_7−δ superconductors

Abstract

We have investigated the effects of oxygen deficiency (δ) on the transition temperature (T _c) of (Sm, Er)Ba₂Cu₃O₇₋ δ superconductors by incorporating the effects of the two dimensional (2D) acoustic phonons and plasmons in the framework of strong coupling theory. The proposed approach for yttrium cuprates properly takes care of the double CuO₂ plane in a unit cell and has been found earlier to be successful in describing the pairing mechanism as well as the variation ofT _c withδ in Y Ba₂Cu₃O₇₋ δ system. The coupling strength (λ), the screening parameter (μ*) and the two dimensional acoustic phonon (plasmon) energyħω ₋(ω₊) as a function of oxygen deficiency is worked out. Finally, the transition temperature is evaluated and is found to be consistent with the earlier experimental data on yttrium cuprates. Thus, coupled phonon-plasmon mechanism is adequate to understand the nature of pairing mechanism and oxygen deficiency dependence of transition temperature in 90 K (Sm, Er)Ba₂Cu₃O₇₋ δ superconductors.