Origin of the Pseudogap in High-Temperature Cuprate Superconductors

TL;DR

This paper uses ab initio calculations to show that inhomogeneous CuO2 plaquettes explain the pseudogap phenomenon in high-temperature cuprate superconductors, linking local structure to electronic properties.

Contribution

It introduces a model where inhomogeneous plaquettes cause the pseudogap, supported by quantitative calculations matching experimental data.

Findings

Plaquettes percolate at x ≈ 0.05, enabling superconductivity.

Disconnected plaquettes produce degenerate states at the Fermi level.

Pseudogap magnitude correlates with isolated plaquette distribution.

Abstract

Cuprate high-temperature superconductors exhibit a pseudogap in the normal state that decreases monotonically with increasing hole doping and closes at x \approx 0.19 holes per planar CuO2 while the superconducting doping range is 0.05 < x < 0.27 with optimal Tc at x \approx 0.16. Using ab initio quantum calculations at the level that leads to accurate band gaps, we found that four-Cu-site plaquettes are created in the vicinity of dopants. At x \approx 0.05 the plaquettes percolate, so that the Cu dx2y2/O p{\sigma} orbitals inside the plaquettes now form a band of states along the percolating swath. This leads to metallic conductivity and below Tc to superconductivity. Plaquettes disconnected from the percolating swath are found to have degenerate states at the Fermi level that split and lead to the pseudogap. The pseudogap can be calculated by simply counting the spatial distribution of isolated plaquettes, leading to an excellent fit to experiment. This provides strong evidence in favor of inhomogeneous plaquettes in cuprates.