Quantum Transport Theory with the Nonequilibrium Coherent Potentials

TL;DR

This paper introduces NECPA, a novel theoretical framework combining nonequilibrium Green's functions and coherent potential approximation to analyze disorder effects in quantum transport of nanoelectronic devices.

Contribution

The paper develops NECPA, a new method that extends NEGF with CPA on the complex-time contour, enabling accurate disorder averaging in nonequilibrium quantum transport.

Findings

NECPA accurately predicts disorder effects compared to brute force calculations.

NECPA connects with vertex correction theory on the real-time axis.

Application of NECPA with DFT enables atomistic analysis of nanoelectronic devices.

Abstract

Since any realistic electronic device has some degree of disorder, predicting disorder effects in quantum transport is a critical problem. Here we report the theory of nonequilibrium coherent potential approximation (NECPA) for analyzing disorder effects in nonequilibrium quantum transport of nanoelectronic devices. The NECPA is formulated by contour ordered nonequilibrium Green's function (NEGF) where the disorder average is carried out within the coherent potential approximation on the complex-time contour. We have derived a set of new rules that supplement the celebrated Langreth theorem and, as a whole, the generalized Langreth rules allow us to derive NECPA equations for real time Green's functions. The solution of NECPA equations provide the disorder averaged nonequilibrium density matrix as well as other relevant quantities for quantum transport calculations. We establish the excellent accuracy of NECPA by comparing its results to brute force numerical calculations of disordered tight-binding models. Moreover, the connection of NECPA equations which are derived on the complex-time contour, to the nonequilibrium vertex correction theory which is derived on the real-time axis, is made. As an application, we demonstrate that NECPA can be combined with density functional theory to enable analysis of nanoelectronic device physics from atomistic first principles.