Universality in the ferromagnetic strong coupling regime of the nonequilibrium Kondo model

We present a new method for calculating the time-dependent many-body wavefunction that follows a local quench. In the nonequilibrium Kondo model, we calculate the time-dependent wavefunction and the current-carrying nonequilibrium steady state that is the long time limit (with the system size taken to infinity first). We find a series expression for the steady state current; it agrees with standard leading order results in the usual weak antiferromagnetic regime. The series also allows the identification of a new universal regime of strong ferromagnetic coupling characterized by Kondo temperature T_K^(F) = D exp[ -(3π²/8)ρ|J| ] (J<0, ρ|J| →∞). In this regime, the differential conductance dI/dV reaches the unitarity limit 2e²/h asymptotically at large voltage or temperature [1].

[1] A. B. Culver and N. Andrei, arXiv:1912.00281 and 1912.02956.