Effective SU(2) theory for the pseudogap state

TL;DR

This paper develops an SU(2) theoretical framework for the pseudogap phase in cuprate superconductors, linking fluctuations to Fermi arc formation, pseudogap emergence, and strange metal behavior.

Contribution

It introduces a detailed SU(2) model connecting charge order and superconductivity, revealing new excitonic states and their role in cuprate phase phenomena.

Findings

SU(2) fluctuations are massless in anti-nodal regions.

Fermi arcs and pseudogap are explained by SU(2) fluctuations.

Resonant Excitonic State (RES) accounts for strange metal properties.

Abstract

This paper exposes in a detailed manner the recent findings about the SU(2) scenario for the underdoped phase of the Cuprate superconductors. The SU(2) symmetry is formulated as a rotation between the $d$-wave SC phase and a $d$-wave charge order. We define the operators responsible for the SU(2) rotations and we derive the non-linear $\sigma$-model associated with it. In this framework, we demonstrate that SU(2) fluctuations are massless in finite portions of the Brillouin Zone corresponding to the anti-nodal regions ($0,$$\pi$), ($\pi,0$). We argue that the presence of SU(2) fluctuations in the anti-nodal region leads to the opening of Fermi arcs around the Fermi surface and to the formation of the pseudo-gap. Moreover, we show that SU(2) fluctuations lead, in turn, to the emergence of a finite momentum SC order -or Pair Density Wave (PDW)- and more importantly to a new kind of excitonic particle-hole pairs liquid, the Resonant Excitonic State (RES), which is made of patches of preformed particle-hole pairs with multiple momenta. When the RES liquid becomes critical, we demonstrate that electronic scattering through the critical modes leads to anomalous transport properties. This new finding can account for the Strange Metal (SM) phase at finite temperature, on the right hand side of the SC dome, shedding light on another notoriously mysterious part of the phase diagram of the Cuprates.