Pseudo gap and superconducting gap in the d–p model

Abstract

We investigate pseudo gap and superconducting gap by using the extended self-consistent t-matrix approximation (ESTA) in the d–p model. We take the pairing interaction mediated by the spin fluctuation and calculate the single-particle spectrum, the density of states and the superconducting gap Δ sc( k). The superconducting fluctuation induces excitaion gap Δ fl( k) and large damping of quasi-particles, Γ( k, ω), with d x 2– y 2 symmetry. The effective gap Δ( k), which consists of Δ fl( k) and Δ sc( k), smoothly increases across the superconducting transition temperature T c as T decreases. As the hole-doping rate δ decreases, Δ( k) increases monotonously, while T c has a maximum at δ≅0.11 and decreases in the underdoped region. The damping near the Fermi energy reaches a maximum at T c followed by sharp drop as T decreases. The pseudo gap in the density of states is induced by not only Δ( k) but the ω-dependence of Γ( k, ω).