Superconductivity of overdoped cuprates: the modern face of the ancestral two-electron exchange

TL;DR

This paper proposes that a two-electron exchange mechanism involving Cu 4s and 3d states explains high-temperature superconductivity in overdoped cuprates, fitting experimental data and unifying the pairing mechanism across doping levels.

Contribution

It introduces a detailed BCS-based model based on the two-electron exchange amplitude J_sd as the pairing mechanism in overdoped cuprates, aligning with ARPES data.

Findings

Derived explicit momentum-dependent gap Delta_p fitting ARPES data

Analytically calculated thermodynamic properties like specific heat and penetration depth

Unified pairing mechanism for both overdoped and underdoped cuprates

Abstract

The single-site two-electron exchange amplitude J_sd between the Cu 4s and Cu 3d_{x^2-y^2} states is found to be the pairing mechanism of high-T_c overdoped cuprates. The noninteracting part of the Hamiltonian spans the copper Cu 4s, Cu 3d_{x^2-y^2} and oxygen O 2p_x and O 2p_y states. Within the standard BCS treatment an explicit expression for the momentum dependence of the gap Delta_p is derived and shown to fit the angle-resolved photoemission spectroscopy (ARPES) data. The basic thermodynamic and electrodynamic properties of the model (specific heat C(T), London penetration depth lambda(T)) are analytically derived. These are directly applicable to cuprates without complicating structural accessories (chains, double CuO_2 planes, etc.). We advocate that the pairing mechanism of overdoped and underdoped cuprates is the same, as T_c displays smooth doping dependence. Thus, a long-standing puzzle in physics is possibly solved.