Fluctuation conductivity due to the preformed local pairs

TL;DR

This paper explores how preformed local pairs in a system influence fluctuation conductivity, revealing enhanced diamagnetism and a Drude peak above the superconducting transition temperature due to short-range correlations.

Contribution

It introduces a nonperturbative method to analyze fluctuation conductivity caused by preformed pairs and links these effects to observable magnetic and transport properties.

Findings

Enhanced diamagnetic response above T_c due to preformed pairs

Appearance of the Drude peak within the pseudogap regime

Superconducting correlations detectable in conductivity measurements

Abstract

We investigate 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 \omega <2\Delta_{pg}. Both thes effects are caused above the transition temperature T_c by the short-range superconducting correlations. 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 a.c. and d.c. conductivity.