Extension of the iterated perturbation theory at arbitrary fillings to nonequilibrium steady states

TL;DR

This paper extends the iterated perturbation theory to nonequilibrium steady states away from half filling and benchmarks it against a controlled method, showing good agreement in various regimes.

Contribution

The authors develop a nonequilibrium extension of KK-IPT for arbitrary fillings and validate its accuracy against AMEA, demonstrating its stability and potential usefulness.

Findings

KK-IPT reproduces equilibrium AMEA results with high accuracy.

Good agreement between KK-IPT and AMEA in moderate temperature and bias regimes.

KK-IPT remains stable and potentially useful in low-temperature, low-bias regimes.

Abstract

We extend the Kajueter-Kotliar [Phys. Rev. Lett. 77, 131 (1996)] iterated perturbation theory (KK-IPT) away from half filling to nonequilibrium steady states. We benchmark the resulting nonequilibrium KK-IPT approach against the auxiliary master equation approach (AMEA), whose accuracy is controlled in and out of equilibrium. As expected, in equilibrium, KK-IPT reproduces the AMEA results for different fillings with high accuracy at the level of both spectral properties and electron densities. Out of equilibrium, we study quantum transport across a correlated impurity and compute the differential conductance and spectral functions. We find very good agreement between nonequilibrium KK-IPT and AMEA in the parameter regime where the latter is reliable, in particular at moderate temperatures and biases. These results support nonequilibrium KK-IPT as an approximate description of nonequilibrium steady states away from half filling. Although a controlled benchmark is not available in the low-temperature, low-bias regime, where AMEA becomes less reliable, nonequilibrium KK-IPT remains numerically stable in those regions, suggesting that it may provide a useful alternative for nonequilibrium calculations in this regime.