Nematic Antiferromagnetism and Deconfined Criticality from the Interplay between Electron-Phonon and Electron-Electron Interactions

TL;DR

This paper uses quantum Monte Carlo simulations to explore a model with competing electron-phonon and electron-electron interactions, revealing a novel phase with coexisting orders and evidence of a continuous phase transition with emergent symmetry.

Contribution

It uncovers a new phase with coexisting nematic and antiferromagnetic orders and provides evidence for a Landau-forbidden continuous transition with emergent symmetry.

Findings

Discovery of a coexisting nematic and antiferromagnetic phase.

Evidence of a Landau-forbidden continuous quantum phase transition.

Emergence of O(4) symmetry at the transition.

Abstract

Systems with strong electron-phonon couplings typically exhibit various forms of charge order, while strong electron-electron interactions lead to magnetism. We use determinant quantum Monte Carlo (DQMC) calculations to solve a model on a square lattice with a caricature of these interactions. In the limit where electron-electron interactions dominate it has antiferromagnetic (AF) order, while where electron-phonon coupling dominates there is columnar valence-bond solid (VBS) order. We find a novel intervening phase that hosts coexisting nematic and antiferromagnetic orders. We have also found evidence of a Landau-forbidden continuous quantum phase transition with an emergent $O(4)$ symmetry between the VBS and the nematic antiferromagnetic phases.