Simple approximations to impurities with correlated electrons fail out of equilibrium, leading to an unphysical hysteresis loop in the current-voltage characteristics. Electron correlations are known to suppress this hysteresis. We applied a two-particle semianalytic approach to an out-of-equilibrium Anderson impurity attached to two biased metallic leads. The theory qualitatively correctly interpolates between weak and strong coupling. It is based on reduced parquet equations adapted to capture the critical regions of singularities in the Bethe-Salpeter equations. This advanced approach covers one-particle and two-particle thermodynamic and spectral quantities relatively well in both weak and strong coupling. Our approximation successfully suppressed the unphysical hysteresis loop. Furthermore, we qualitatively reproduced within the linear response the three transport regimes with the increasing temperature: from the Kondo resonant tunneling through the Coulomb-blockade regime up to a sequential tunneling regime. Far from equilibrium, we find that the bias plays a similar role as the temperature in destroying the Kondo resonant peak when the corresponding energy scale is comparable with the Kondo temperature. Aside from that, the applied voltage in low bias was shown to develop spectral peaks around the lead chemical potentials as observed in previous theoretical and experimental studies.
Contact person: Václav Janiš