Charge order and emergent symmetries in cuprate superconductors

TL;DR

This paper explores the phase diagram of cuprate superconductors using field-theoretical models, revealing emergent symmetries and gauge fields that explain complex phenomena like charge order, pseudogap transition, and experimental spectroscopic signatures.

Contribution

It introduces an exact SU(2) symmetry model and an emergent U(1) gauge field framework to unify understanding of charge order, pseudogap, and vortex core phenomena in cuprates.

Findings

Emergent SU(2) symmetry relates superconducting and charge orders.

Skyrmions are predicted inside vortex cores.

Incoherent bosons may cause a jamming transition at optimal doping.

Abstract

In this paper, we present our studies of the phase diagram of the cuprate superconductors performed in recent years. We describe how a few field-theoretical concepts can be used to account for the puzzling properties of these compounds. Starting with a short exposition of recent experimental developments, we then introduce the concept of an emergent SU(2) symmetry, which rotates between the superconducting and charge order parameters. We describe a solvable model for which this symmetry turns out to be exact and derive the corresponding effective field theory in terms of a non-linear {\sigma} model. We then turn to the experimental consequences of our model with the presence of skyrmions inside the vortex core and an elegant account of the B-T phase diagram. Next, we move on to the second concept, which is the one of an emergent U(1) gauge field in the theory. Within this more general framework, the pseudogap transition can be viewed as a confining/deconfining transition. Experimental consequences for a few spectroscopic probes like inelastic neutron scattering, Raman spectroscopy, phonon line in x-ray scattering and angle-resolved photoemission experiments are studied. This theory suggests the presence of incoherent bosons at moderate temperatures in the phase diagram of the cuprates, which would undergo a jamming transition at optimal doping [1]. Consequences of the presence of such bosons on the transport properties of these materials are examined.