Phase Separation and Superconductivity in the Copper Oxide Chain

TL;DR

This paper investigates the phase diagram of copper-oxide chains, revealing conditions for phase separation and superconductivity, and analyzing the effects of Coulomb interactions and valence fluctuations.

Contribution

It provides a detailed analysis of phase separation, superconducting correlations, and charge-density wave formation in copper-oxide chains, including theoretical calculations of correlation exponents.

Findings

Phase separation occurs above a critical Coulomb interaction V.

Superconducting correlations are strongest near the phase boundary.

A charge-density wave forms at n=1 for V > t.

Abstract

The phase diagram of the copper-oxide chain as a function of density and the nearest-neighbour Coulomb interaction, V, is determined. Phase separation takes place above a critical value of $V$ when the Cu2+ to Cu+ valence fluctuations dominate. In the proximity of the phase separation boundary the superconducting correlations are the most divergent. We identify the parameter regions where the Luttinger Liquid theory applies and calculate the contours of the charge-charge correlation exponent K_{\rho}. We show that anomalous flux quantization occurs as$K_{\rho} diverges. At n = 1, for V > t, a gap opens in the spectrum and the ground state is a charge-density wave.