Andreev reflections in the pseudogap state of cuprate supercondcutors

TL;DR

This paper predicts that Andreev reflection occurs in the pseudogap state of cuprate superconductors due to preformed pairs, suggesting a way to detect these pairs above the superconducting transition temperature.

Contribution

It introduces a theoretical framework for Andreev reflection in the pseudogap state, providing quantitative calculations and proposing experimental signatures.

Findings

Andreev reflection can occur above Tc in pseudogap state

Enhanced tunneling conductance below the gap observed experimentally

Supports the existence of preformed pairs in the pseudogap phase

Abstract

We propose that, if the pseudogap state in the cuprate superconductors can be described in terms of the phase-incoherent preformed pairs, there should exist Andreev reflection from these pairs even above the superconducting transition temperature, $T_c$. After giving qualitative arguments for this effect, we present more quantitative calculations based on the Bogoliubov--de Gennes equation. Experimental observations of the effects of Andreev reflections above $T_c$---such as an enhanced tunneling conductance below the gap along the copper oxide plane---could provide unambiguous evidence for the preformed pairs in the pseudogap state.