Competition between superconductivity and charge density waves

TL;DR

This paper develops an effective field theory using SO(3) pseudospin representation to study the competition between superconductivity and charge density waves, revealing a Berry phase and a deconfined quantum critical point with fractionalized charge excitations.

Contribution

It introduces a nonlinear sigma model with Berry phase effects that resolves previous conflicts and demonstrates the existence of a deconfined quantum critical point with fractionalized charges at half filling.

Findings

Berry phase emerges at half filling, influencing the SC-CDW transition.

Deconfined quantum critical point with fractional charge e is identified.

Deconfinement persists even with weak quenched disorder.

Abstract

We derive an effective field theory for the competition between superconductivity (SC) and charge density waves (CDWs) by employing the SO(3) pseudospin representation of the SC and CDW order parameters. One important feature in the effective nonlinear $\sigma$ model is the emergence of Berry phase even at half filling, originating from the competition between SC and CDWs, i.e., the pseudospin symmetry. A well known conflict between the previous studies of Oshikawa\cite{Oshikawa} and D. H. Lee et al.\cite{DHLee} is resolved by the appearance of Berry phase. The Berry phase contribution allows a deconfined quantum critical point of fractionalized charge excitations with $e$ instead of $2e$ in the SC-CDW quantum transition at half filling. Furthermore, we investigate the stability of the deconfined quantum criticality against quenched randomness by performing a renormalization group analysis of an effective vortex action. We argue that although randomness results in a weak disorder fixed point differing from the original deconfined quantum critical point, deconfinement of the fractionalized charge excitations still survives at the disorder fixed point owing to a nonzero fixed point value of a vortex charge.