Thermodynamic and Dynamical Signatures of a Quantum Spin-Hall Insulator to Superconductor Transition

TL;DR

This paper investigates the thermodynamic and dynamical properties of a Dirac fermion model undergoing a quantum phase transition from a quantum spin-Hall insulator to a superconductor, revealing emergent excitations and symmetries.

Contribution

It provides a detailed quantum Monte Carlo study of the DQCP, highlighting emergent spinons, skyrmions, and Lorentz symmetry at the transition.

Findings

Linear temperature dependence of susceptibilities due to emergent excitations

Similarity in dynamic structure factors supporting emergent Lorentz symmetry

Superconductivity destroyed by spin-1/2 vortex proliferation at high temperature

Abstract

Thermodynamic and dynamical properties of a model of Dirac fermions with a deconfined quantum critical point (DQCP) separating an interaction-generated quantum spin-Hall insulator from an s-wave superconductor [Nature Comm.~{\bf 10}, 2658 (2019)] are studied by quantum Monte Carlo simulations. Inside the deconfined quantum critical region bound by the single-particle gap, spinons and spinless charge-2e skyrmions emerge. Since the model conserves total spin and charge, and has a single length scale, these excitations lead to a characteristic linear temperature dependence of the uniform spin and charge susceptibilities. At the DQCP, the order parameter dynamic structure factors show remarkable similarities that support emergent Lorentz symmetry. Above a critical temperature, superconductivity is destroyed by the proliferation of spin-1/2 vortices.