# Non-equilibrium Green's functions and their relation to the negative differential conductance in the interacting resonant level model

## TL;DR

This paper investigates the non-equilibrium spectral properties and current-voltage behavior of the interacting resonant level model, revealing how spectral changes relate to negative differential conductance and impurity decoupling at high bias.

## Contribution

It provides nonperturbative, accurate Green's function calculations for the IRLM under bias, linking spectral evolution to NDC and impurity decoupling mechanisms.

## Key findings

- Spectral properties change drastically between low and high bias regimes.
- Negative differential conductance correlates with impurity decoupling from leads.
- Distribution functions show anomalous evolution near the impurity.

## Abstract

We evaluate the non-equilibrium single particle Green's functions in the steady state of the interacting resonant level model (IRLM) under the effect of an applied bias voltage. Employing the so-called auxiliary master equation approach, we present accurate nonperturbative results for the non-equilibrium spectral and effective distribution functions, as well as for the current-voltage characteristics. We find a drastic change of these spectral properties between the regimes of low and high bias voltages and discuss the relation of these changes to the negative differential conductance (NDC), a prominent feature in the non-equilibrium IRLM. The anomalous evolution of the distribution function next to the impurity shown by our calculations suggests a mechanism whereby the impurity gets effectively decoupled from the leads at voltages where the NDC sets in, in agreement with previous renormalization group approaches. This scenario is qualitatively confirmed by a Hartree-Fock treatment of the model.