Fluctuation conductivity due to the preformed local pairs

Abstract

We investigated the properties of a system where the itinerant electrons coexist and interact with the preformed local pairs. Using the nonperturbative continuous unitary transformation technique we show that Andreev-type scattering between these charge carriers gives rise to the enhanced diamagnetic response and is accompanied by appearance of the Drude peak inside the pseudogap regime ω ≤ 2∆ pg . Both effects are caused by the short-range superconducting correlations above the transition temperature T c . In fact, the residual diamagnetism has been detected by the torque magnetometry in the lanthanum and bismuth cuprate superconductors at temperatures up to ~ 1.5T c . In this work we show how the superconducting correlations can be observed in the ac and dc conductivity.