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

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.