The Disordered Induced Interaction and the Phase Diagram of Cuprates

TL;DR

This paper introduces a disordered induced interaction mechanism in cuprates, explaining their phase diagram, pseudogap phase, and local density of states variations through local free energy minimization and charge inhomogeneity.

Contribution

It proposes a novel process driven by local free energy minimization that explains charge inhomogeneity and two-step superconducting transition in cuprates.

Findings

Reproduces main features of cuprates phase diagram

Provides interpretation of pseudogap phase

Matches local density of states measurements

Abstract

There are processes in nature that resemble a true force but arise due to the minimization of the local energy. The most well-known case is the exchange interaction that leads to magnetic order in some materials. We discovered a new similar process occurring in connection with an electronic phase separation transition that leads to charge inhomogeneity in cuprate superconductors. The minimization of the local free energy, described here by the Cahn-Hilliard diffusion equation, drives the charges into regions of low and high densities. This motion leads to an effective potential with two-fold effect: creation of tiny isolated regions or micrograins, and two-body attraction, which promotes local or intra-grain superconducting pairing. Consequently, as in granular superconductors, the superconducting transition appears in two steps. First, with local intra-grain superconducting amplitudes and, at lower temperature, the superconducting phase or resistivity transition is attained by intergrain Josephson coupling. We show here that this approach reproduces the main features of the cuprates phase diagram, gives a clear interpretation to the pseudogap phase and yields the position dependent local density of states gap $\Delta(\vec r)$ measured by tunnelling experiments.