Response Time in High-Frequency Quantum Transport

Abstract

The theory of quantum transport is the theoretical basis for nanostructure devices. In the last few years, the theory of quantum transport has been extensively discussed, developed, and tested [1]. Much of this discussions, however, has been centered on DC transport. The question naturally arises as to whether, and if so to what extent, we can generalize the results of DC Quantum transport theory and apply them in the high frequency regime. In this paper we study this question. Specifically, we consider the question of the intrinsic time scale of AC operation. Just like the drift diffusion process in a conventional semiconductor device sets one such time scale, so too do various physical processes in a quantum device. We concentrate on two such processes: the RC response and the time scale related to tunneling (see below). It will become clear in the following that this problem is a complicated one; while various formulations in the literature capture some aspects of the problem, a complete description does not appear possible, and any oversimplification can only lead to erroneous results.