Pseudogaps in Underdoped Cuprates

TL;DR

This paper reviews experimental evidence of pseudogaps in underdoped cuprates, discusses their interpretation via a doped Mott insulator framework, and introduces a quasiparticle-based model derived from the t-J model.

Contribution

It presents a new quasiparticle model based on the t-J model that predicts doping dependence of T_c and energy-gap ratios, and discusses a transition from U(1) to SU(2) formulations.

Findings

Pseudogaps affect magnetic and c-axis properties but not in-plane transport.

The quasiparticle model predicts doping-dependent T_c and energy-gap ratios.

SU(2) formulation resolves issues in the U(1) approach.

Abstract

It has become clear in the past several years that the cuprates show many unusual properties, both in the normal and superconducting states, especially in the underdoped region. In particular, gap-like behavior is observed in magnetic properties, c-axis conductivity and photoemission, whereas in-plane transport properties are only slightly affected by the pseudogap. I shall argue that these experimental evidences must be viewed in the context of the physics of a doped Mott insulator and that they support the notion of spin charge separation. I shall review recent theoretical developments, concentrating on studies based on the t-J model. I shall describe a model based on quasiparticle excitations, which predicts the doping dependence of T_c and anomalous energy-gap-to-T_c ratios. Finally, I shall outline how the model may be derived from a microscopic formulation of the t-J model. After a brief review of the U(1) formulation, I shall explain some of the difficulties encountered there, and how a new SU(2) formulation can resolve some of the difficulties.