Dynamical transport measurements of a quantum point contact in GHz

Abstract

We report the time-dependent measurements in a ballistic quantum point contact at gigahertz frequencies. The Nyquist curves (Im(G) versus Re(G)) of the admittance show a general quadratic function, which extend the linear behaviour reported by Gabelli et al. in the previous experiment. We find that the deviations from the linear behaviour in Nyquist curves are increased with the conductance and the strength of the applied magnetic filed. The Nqyquist curves give direct access to the relaxation time in a quantum RL circuit, which governs the dynamic response of the circuit. The oringin of the deviations is that the geometric capacitance is much smaller than the quantum capacitance of a single quantum point contact device. Hence, our results demonstrate that the dynamic transport strongly depends on the geometric structure of the mesoscopic structures.