The enigma of the pseudogap phase of the cuprate superconductors

TL;DR

This paper reviews recent experimental findings on cuprate superconductors, highlighting evidence for a d-form factor density-wave order and proposing a fractionalized Fermi liquid as a key feature of the pseudogap phase.

Contribution

It synthesizes experimental data to support the existence of a d-form factor density-wave and introduces the FL* model to explain the pseudogap phase in cuprates.

Findings

Evidence for d-form factor density-wave order in non-Lanthanum cuprates

Proposal of a fractionalized Fermi liquid (FL*) with four spin-1/2 pockets

Insights into the electronic structure of the pseudogap phase

Abstract

The last few years have seen significant experimental progress in characterizing the copper-based hole-doped high temperature superconductors in the regime of low hole density, p. Quantum oscillations, NMR, X-ray, and STM experiments have shed much light on the nature of the ordering at low temperatures. We review evidence that the order parameter in the non-Lanthanum-based cuprates is a d-form factor density-wave. This novel order acts as an unexpected window into the electronic structure of the pseudogap phase at higher temperatures in zero field: we argue in favor of a `fractionalized Fermi liquid' (FL*) with 4 pockets of spin S=1/2, charge +e fermions enclosing an area specified by p.