A Coherent RC Circuit

TL;DR

This paper experimentally investigates the ac conductance of a quantum RC circuit, confirming theoretical predictions about quantum capacitance and charge relaxation resistance, and revealing quantum effects in electron dwell times and capacitance oscillations.

Contribution

It provides the first experimental validation of the quantum RC circuit model, linking ac conductance to electron dwell time and demonstrating quantum oscillations in capacitance.

Findings

Quantum capacitance relates to the density of states.

Charge relaxation resistance remains constant at h/2e^2.

Capacitance oscillates as transmission decreases.

Abstract

We review the first experiment on dynamic transport in a phase-coherent quantum conductor. In our discussion, we highlight the use of time-dependent transport as a means of gaining insight into charge relaxation on a mesoscopic scale. For this purpose, we studied the ac conductance of a model quantum conductor, i.e. the quantum RC circuit. Prior to our experimental work, M. B\"{u}ttiker, H. Thomas and A. Pr\^{e}tre first worked on dynamic mesoscopic transport in the 1990s. They predicted that the mesoscopic RC circuit can be described by a quantum capacitance related to the density of states in the capacitor and a constant charge relaxation resistance value equal to half of the resistance quantum h/2e^2, when a single mode is transmitted between the capacitance and a reservoir. By applying a microwave excitation to a gate located on top of a coherent submicronic quantum dot that is coupled to a reservoir, we validate this theoretical prediction on the ac conductance of the quantum RC circuit. Our study demonstrates that the ac conductance is directly related to the dwell time of electrons in the capacitor. Thereby, we observed a counterintuitive behavior of a quantum origin: as the transmission of the single conducting mode decreases, the resistance of the quantum RC circuit remains constant while the capacitance oscillates.