Attenuation and amplification of the transient current in nanojunctions with time-varying gate potentials

TL;DR

This paper investigates how time-varying gate potentials influence charge transport in nanojunctions, revealing phenomena like current induction without bias, attenuation or amplification of net current, and dynamic relaxation effects.

Contribution

It introduces a Green's function-based method to analyze transient current responses to time-dependent gate potentials in nanojunctions, highlighting non-instantaneous and oscillatory behaviors.

Findings

Gate potential can induce current without bias

Net current can be attenuated or amplified by gate sign

System response exhibits relaxation time and oscillations

Abstract

We study charge transport in a source-channel-drain system with a time-varying applied gate potential acting on the channel. We calculate both the current flowing from the source into the channel and out of the channel into the drain. The current is expressed in terms of nonequilibrium Green's functions. These nonequilibrium Green's functions can be determined from the steady-state Green's functions and the equilibrium Green's functions of the free leads. We find that the application of the gate potential can induce current to flow even when there is no source-drain bias potential. However, the direction of the current from the source and the current to the drain are opposite, thereby resulting in no net current flowing within the channel. When a source-drain bias potential is present, the net current flowing to the source and drain can either be attenuated or amplified depending on the sign of the applied gate potential. We also find that the response of the system to a dynamically changing gate potential is not instantaneous, i.e., a relaxation time has to pass before the current settles into a steady value. In particular, when the gate potential is in the form of a step function, the current first overshoots to a maximum value, oscillates, and then settles down to a steady-state value.