Pseudo-spin Skyrmions in the Phase Diagram of Cuprate Superconductors

TL;DR

This paper proposes that skyrmions in pseudo-spin space, related to an SU(2) symmetry, explain the complex phase diagram and properties of the pseudogap phase in under-doped cuprate superconductors.

Contribution

It introduces a topological skyrmion-based framework involving SU(2) symmetry to elucidate the pseudogap, superconducting, and charge modulation phases in cuprates.

Findings

Charge modulations inside vortex cores are consistent with skyrmion structures.

The SU(2) symmetry controls phase transitions and the pseudogap phenomena.

The theory explains gapping in the anti-nodal region and phase transitions with nematic and loop current characters.

Abstract

Topological states of matter are at the root of some of the most fascinating phenomena in condensed matter physics. Here we argue that skyrmions in the pseudo-spin space related to an emerging SU(2) symmetry enlighten many mysterious properties of the pseudogap phase in under-doped cuprates. We detail the role of the SU(2) symmetry in controlling the phase diagram of the cuprates, in particular how a cascade of phase transitions explains the arising of the pseudogap, superconducting and charge modulation phases seen at low temperature. We specify the structure of the charge modulations inside the vortex core below $T_{c}$, as well as in a wide temperature region above $T_{c}$, which is a signature of the skyrmion topological structure. We argue that the underlying SU(2) symmetry is the main structure controlling the emergent complexity of excitations at the pseudogap scale $T^{*}$. The theory yields a gapping of a large part of the anti-nodal region of the Brillouin zone, along with $q=0$ phase transitions, of both nematic and loop currents characters.