Origin of the T$_c$ enhancement in heterostructure cuprate superconductors

TL;DR

This paper explains the T$_c$ enhancement in heterostructure cuprate superconductors as a result of structural changes increasing apical oxygen distance, which enhances superconductivity through modifications in the extended Hubbard model.

Contribution

It provides a theoretical explanation linking lattice structural changes to T$_c$ enhancement in heterostructure cuprates, supported by model calculations.

Findings

Structural change increases apical oxygen distance.

Enhanced off-site interaction boosts d-wave superconductivity.

Model calculations support the proposed mechanism.

Abstract

Recent experiments on heterostructures composed of two or more films of cuprate superconductors of different oxygen doping levels\cite{Yuli,Gozar} have shown a remarkable T$_c$ enhancement (up to 50%) relative to single compound films. We provide here a simple explanation of the enhancement which arises naturally from a collection of experimental works. We show that the enhancement could be caused by a structural change in the lattice, namely an increase in the distance of the apical oxygen from the copper-oxygen plane. This increase modifies the effective off-site interaction in the plane which in turn enhances the d-wave superconductivity order parameter. To illustrate this point we study the extended Hubbard model using the fluctuation exchange approximation.