Quantum-critical dynamics of a Josephson junction at the topological transition

TL;DR

This paper investigates the universal electromagnetic response of a Josephson junction at a topological transition, revealing unique low-energy dissipation behavior and scaling properties governed by system symmetries.

Contribution

It provides a theoretical analysis of the admittance near a topological transition, highlighting universal features and the impact of symmetries on the dissipative response.

Findings

Re Y(ω) ∝ max(ω, T)^2 at the critical point

Universal admittance dependence determined by symmetries

Scaling functions controlled by at most two parameters away from criticality

Abstract

We find the admittance $Y(\omega)$ of a Josephson junction at or near a topological transition. The dependence of the admittance on frequency and temperature at the critical point is universal and determined by the symmetries of the system. Despite the absence of a spectral gap at the transition, the dissipative response may remain weak at low energies: $\mathrm{Re}\,Y(\omega)\propto \max (\omega, T)^2$. This behavior is strikingly different from the electromagnetic response of a normal metal. Away from the critical point, the scaling functions for the dependence of the admittance on frequency and temperature are controlled by at most two parameters.