Instabilities near the onset of spin density wave order in metals

TL;DR

This paper explores the low energy behavior of two-dimensional metals near spin density wave order, revealing an emergent symmetry that links superconducting pairing to a modulated bond order instability.

Contribution

It introduces a nearly competing bond order instability arising from an emergent pseudospin symmetry in the low energy theory.

Findings

Identification of a nearly as strong bond order instability

Connection between pairing amplitude sign change and bond order via pseudospin symmetry

Insight into competing orders near spin density wave transition

Abstract

We discuss the low energy theory of two-dimensional metals near the onset of spin density wave order. It is well known that such a metal has a superconducting instability induced by the formation of spin-singlet pairs of electrons, with the pairing amplitude changing sign between regions of the Fermi surface connected by the spin density wave ordering wavevector. Here we review recent arguments that there is an additional instability which is nearly as strong: towards the onset of a modulated bond order which is locally an Ising-nematic order. This new instability is a consequence of an emergent "pseudospin" symmetry of the low energy theory---the symmetry maps the sign-changing pairing amplitude to the bond order parameter.