Deconfined Thermal Phase Transitions with $Z_2$ Gauge Structures

TL;DR

This paper explores exotic thermal phase transitions in deconfined $Z_2$ gauge phases, revealing new phenomena like thermal confinement transitions and unconventional symmetry breaking, with implications for quantum spin liquids and topological orders.

Contribution

It constructs a $Z_2$ lattice gauge model demonstrating thermal phase transitions in 2D, and analyzes the effects of deconfined fermions and symmetry breaking beyond traditional theories.

Findings

Existence of a thermal phase transition between deconfined and confined phases in 2D.

Deconfined fermions induce gapless excitations and line-tension effects.

Symmetry breaking transitions can be unconventional and in the same universality class.

Abstract

Fathoming deconfined phases is one of the key issues in modern condensed matter. Striking many-body effects including massive quantum entanglement and coherence may be realized as manifested in quantum spin liquids and topological orders. Here, we demonstrate that deconfined phases even host exotic thermal phase transitions, dubbed deconfined thermal transitions. Constructing a $Z_2$ lattice gauge model with strong interactions between $Z_2$ gauge fluxes, we prove the existence of a thermal phase transition between deconfined and confined phases in two spatial dimensions in sharp contrast to its absence in the Wegner model. Incorporating deconfined fermions, it is shown that gapless excitations from Fermi surfaces endow line-tension to $Z_2$ gauge fluxes at zero temperature, and we argue that a deconfined thermal transition with deconfined fermions may be interpreted as a hidden order transition with thermal gap-opening in Fermi surfaces. Moreover, it is shown that symmetry breaking transitions in deconfined phases may be unconventional. Global $Z_2$ and $U(1)$ symmetry breaking transitions in deconfined phases may be in the same universality class, which is impossible under the conventional Landau-Ginzburg-Wilson paradigm. Characteristic signatures of the transitions in experiments and candidate strongly correlated systems such as Kitaev materials are also discussed.