Theory of Underdoped Cuprates

TL;DR

This paper develops an SU(2) symmetric slave-boson theory for the t-J model at finite doping, explaining various phases of cuprate superconductors and their evolution with doping.

Contribution

It introduces a novel SU(2) symmetric mean field approach to the t-J model that captures multiple phases observed in cuprates.

Findings

Consistent phase diagram with cuprate phases

Identification of the spin gap as a staggered flux phase

Evolution of Fermi pockets into a large Fermi surface with doping

Abstract

We develop a slave-boson theory for the t-J model at finite doping which respects an SU(2) symmetry -- a symmetry previously known to be important at half filling. The mean field phase diagram is found to be consistent with the phases observed in the cuprate superconductors, which contains d-wave superconductor, spin gap, strange metal, and Fermi liquid phases. The spin gap phase is best understood as the staggered flux phase, which is nevertheless translationally invariant for physical quantities. The electron spectral function shows small Fermi pockets at low doping which continuously evolve into the large Fermi surface at high doping concentrations.