Magnetic Behavior of the Cuprate Superconductors

TL;DR

This paper reviews a universal model for magnetic dynamics in high-temperature cuprate superconductors, explaining various experimental phenomena through a dual excitations framework.

Contribution

It introduces a model combining antiferromagnetic spin waves and Fermi-liquid quasiparticles, unifying different phases and explaining the spin gap phenomenon.

Findings

The model reproduces z=1 and z=2 universality classes.

It explains the spin gap phenomenon.

The theory is consistent with experimental and microscopic data.

Abstract

I review recent work on magnetic dynamics of the high temperature superconductors using a model that combines two weakly interacting species of low-energy excitations: the antiferromagnetic spin waves which carry spin-1 and no charge, and Fermi-liquid-like quasiparticles which carry spin-1/2 and charge e. The model allows conversion of spin waves into electron-hole pairs; however, the low-energy spin waves are not collective modes of the quasiparticles near the Fermi surface, but rather are a separate branch of the low-energy spectrum. With certain experimentally justified assumptions, this theory is remarkably universal: the dependence on the detailed microscopic Hamiltonian and on doping can be absorbed into several experimentally measurable parameters. The z=1 theory of the insulators and z=2 theory of the overdoped materials, are both reproduced as limiting cases of the theory described here, which predicts that the underdoped materials remain in z=1 universality class at sufficiently high temperature. This theory provides a framework for understanding both the experimental results and microscopic calculations, and in particular yields a possible explanation of the spin gap phenomenon. I also discuss some of the important unresolved issues.