Superconductivity in the presence of pseudogap: Strong-coupling approach

We discuss the structure of the pseudogap, which originates from the charge -density wave (CDW). For imperfect nesting the density of states at Fermi l evel remains finite despite the opening of the CDW gap. Its depth depends o n the concentration of holes and decreases with doping. This property can s ignificantly affect the competition between CDW and superconductivity. We a pply the Eliashberg equations and obtain analytical results for the superco nducting transition temperature in the presence of the pseudogap of arbitra ry magnitude and depth. We demonstrate that the isotope effects for the sup erconducting transition temperature (cr) and the pseudogap (alpha*) are inv ersely correlated with each other, In particular, doping dependence of the superconducting isotope effect observed in underdoped high-temperature supe rconductors, can originate from opening of the normal-state pseudogap, prov ided that alpha* < 1/2. (C) 2001 Elsevier Science B.V. All rights reserved.