Antiferromagnetism in metals: from the cuprate superconductors to the heavy fermion materials

TL;DR

This paper reviews the critical theory of antiferromagnetism in metals, its connection to unconventional superconductivity, and explores phases like the fractionalized Fermi liquid relevant to cuprates and heavy fermion systems.

Contribution

It provides a unified analysis of antiferromagnetic quantum criticality, superconductivity enhancement, and introduces the concept of a fractionalized Fermi liquid phase in correlated metals.

Findings

Logarithm-squared enhancement of pairing vertex near criticality

Universal coefficient for pairing enhancement independent of interaction strength

Proposal of a fractionalized Fermi liquid phase without magnetic order

Abstract

The critical theory of the onset of antiferromagnetism in metals, with concomitant Fermi surface reconstruction, has recently been shown to be strongly coupled in two spatial dimensions. The onset of unconventional superconductivity near this critical point is reviewed: it involves a subtle interplay between the breakdown of fermionic quasiparticle excitations on the Fermi surface, and the strong pairing glue provided by the antiferromagnetic fluctuations. The net result is a logarithm-squared enhancement of the pairing vertex for generic Fermi surfaces, with a universal dimensionless co-efficient independent of the strength of interactions, which is expected to lead to superconductivity at the scale of the Fermi energy. We also discuss the possibility that the antiferromagnetic critical point can be replaced by an intermediate `fractionalized Fermi liquid' phase, in which there is Fermi surface reconstruction but no long-range antiferromagnetic order. We discuss the relevance of this phase to the underdoped cuprates and the heavy-fermion materials.