Two-component scenario and related gaps in cuprates

TL;DR

This paper presents a simple model of cuprate superconductivity involving a two-component defect subsystem and doping-dependent band overlaps, explaining various experimental phenomena including pseudogaps, superconducting gaps, and the insulator-metal transition.

Contribution

It introduces a novel two-component defect model with doping-dependent gaps and band overlaps, providing qualitative explanations for multiple experimental observations in cuprates.

Findings

Presence of two pseudogaps at underdoping

Manifestation of two superconducting gaps at overdoping

Superconducting transition temperature (Tc) peaks near optimal doping

Abstract

A simple model of cuprate superconductivity with an electron spectrum prepared by doping is developed. The pair-transfer interaction couples the itinerant band with two components ("hot'' and "cold'') of the defect subsystem. There are basic defect-itinerant gaps quenched by progressive doping. Band overlaps appear as novel sources for critical doping concentrations. Insulator to metal transitions in the normal state are expected here. Minimal quasiparticle excitation energies determine the pseudo- and superconducting gaps according to the doping-dependent disposition of bands. Two pseudogaps can be present at underdoping and two superconducting gaps can be manifested at overdoping. Various transformations and connections between the gaps agree qualitatively with versatile experimental findings. The superconducting density does not reflect the presence of "extrinsic'' gaps because of the interband nature of the pairing. A Uemura type sublinear plot at underdoping with further recession is obtained. A mixed Fermi-liquid is restored near optimal doping where the chemical potential intersects all the band components. The metallization of the "cold'' subsystem is essential for the rise of Tc on passing to optimal dopings.