A gauge-invariant and current-continuous microscopic ac quantum transport theory

TL;DR

This paper develops a gauge-invariant, current-continuous microscopic ac quantum transport theory based on non-equilibrium Green's functions, clarifying key concepts and validating the approach with first-principles calculations.

Contribution

It introduces a new formalism for ac quantum transport that ensures gauge invariance and current continuity, addressing limitations of previous models.

Findings

The new formalism satisfies gauge invariance and current continuity.

Validation through first-principles calculations on a carbon nanotube device.

The traditional expression for dynamic admittance is recovered only under specific conditions.

Abstract

There had been consensus on what the accurate ac quantum transport theory was until some recent works challenged the conventional wisdom. Basing on the non-equilibrium Green's function formalism for time-dependent quantum transport, we derive an expression for the dynamic admittance that satisfies gauge invariance and current continuity, and clarify the key concept in the field. The validity of our now formalism is verified by first-principles calculation of the transient current through a carbon-nanotube-based device under the time-dependent bias voltage. Moreover, the previously well-accepted expression for dynamic admittance is recovered only when the device is a perfect conductor at a specific potential.