Superradiant phase transition in electronic systems and emergent topological phases

TL;DR

This paper establishes a general criterion for superradiant phase transitions in electronic systems coupled to cavity fields, demonstrating conditions under which they occur or are prevented, and revealing emergent topological phases in specific models.

Contribution

It provides a universal criterion for superradiant phase transitions in electronic systems, extending no-go theorems and identifying conditions for topological phases to emerge.

Findings

Longitudinal superradiance is always prevented in 2D and 1D systems.

Superradiant phases can occur with nonuniform transverse cavity fields in certain models.

Emergent topological phases include Dirac points with zero-modes and Chern insulators.

Abstract

We derive a general criterion for determining the onset of superradiant phase transition in electronic bands coupled to a cavity field, with possibly electron-electron interactions. For longitudinal superradiance in 2D or genuine 1D systems, we prove that it is always prevented, thereby extending existing no-go theorems. Instead, a superradiant phase transition can occur to a nonuniform transverse cavity field and we give specific examples in non-interacting models, either through Fermi surface nesting or parabolic band touching. Investigating the resulting time-reversal symmetry breaking superradiant states, we find in the former case Fermi surface lifting down to four Dirac points on a square lattice model, with topologically protected zero-modes, and in the latter case topological bands with non-zero Chern number on an hexagonal lattice.