Non-linear Conductance for the Charge Two-Channel Kondo Model

Motivated by a recent experiment [Z. Iftikhar et al, Nature 526, 233 (2015)], we report a time-dependent Density-Matrix Renormalization-Group computation of the low-temperature non-equilibrium current across a microscopic metallic island coupled to two independent leads. At low T, the nearly complete freezing of the island degrees of freedom leaves only two degenerate states, whose charges differ by one electron. The dynamics of charge conduction through the island is modeled by an anisotropic two-channel Kondo Hamiltonian, in which the two impurity-spin components represent the island states, a spin flip emulating the transfer of one electron to or from the leads. We have computed the current, following the application of a sudden bias eV, over time intervals substantially longer than the characteristic time \hbar/(eV), albeit short on the Kondo time scale. For symmetric couplings, plotted as a function of eV, the differential conductances show universal behavior. For asymmetric couplings, the differential conductances display the expected crossover from Fermi-liquid to non-Fermi-liquid behavior as eV grows.