Symmetry Protected Topological Metals

TL;DR

This paper demonstrates that topological quantum phase transitions can occur between gapless metallic states with extended Fermi surfaces, protected by symmetry, and characterized by discontinuous transport coefficient jumps.

Contribution

It introduces a model showing symmetry-protected topological transitions between metallic states, expanding the understanding of topological phases beyond gapped systems.

Findings

Transition characterized by discontinuous off-diagonal transport coefficient

Transition protected by unbroken symmetry such as particle-hole symmetry

Model based on 2D p+ip superconductor with supercurrent

Abstract

We show that sharply defined topological quantum phase transitions are not limited to states of matter with gapped electronic spectra. Such transitions may also occur between two gapless metallic states both with extended Fermi surfaces. The transition is characterized by a discontinuous, but not quantized, jump in an off-diagonal transport coefficient. Its sharpness is protected by a symmetry, such as e.g. particle-hole, which remains unbroken across the transition. We present a simple model of this phenomenon, based on 2D $p+ip$ superconductor with an applied supercurrent, and discuss its geometrical interpretation.