Self-consistent ac quantum transport using nonequilibrium Green functions

TL;DR

This paper presents a self-consistent ac quantum transport method using nonequilibrium Green's functions, crucial for accurately modeling high-frequency behaviors and plasmonic effects in nanoscale devices like nanotube transistors.

Contribution

The authors develop a novel self-consistent approach for ac quantum transport that captures dynamic charge-potential feedback and plasmonic excitations in low-dimensional systems.

Findings

Self-consistent feedback is essential for accurate transport modeling.

Plasmon excitations appear as peaks in dynamic conductance at terahertz frequencies.

Off-state conductance shows smooth oscillations, indicating single-particle effects.

Abstract

We develop an approach for self-consistent ac quantum transport in the presence of time-dependent potentials at non-transport terminals. We apply the approach to calculate the high-frequency characteristics of a nanotube transistor with the ac signal applied at the gate terminal. We show that the self-consistent feedback between the ac charge and potential is essential to properly capture the transport properties of the system. In the on-state, this feedback leads to the excitation of plasmons, which appear as pronounced divergent peaks in the dynamic conductance at terahertz frequencies. In the off-state, these collective features vanish, and the conductance exhibits smooth oscillations, a signature of single-particle excitations. The proposed approach is general and will allow the study of the high-frequency characteristics of many other low-dimensional nanoscale materials such as nanowires and graphene-based systems, which are attractive for terahertz devices, including those that exploit plasmonic excitations.