CHARGE-RELAXATION AND DWELL TIME IN THE FLUCTUATING ADMITTANCE OF A CHAOTIC CAVITY

We consider the admittance of a chaotic quantum dot, capacitively coup led to a gate and connected to two electron reservoirs by multichannel ballistic point contacts. For a dot in the regime of weak localizatio n and universal conductance fluctuations, we calculate the average and variance of the admittance using random-matrix theory. We find that t he admittance is governed by two time scales: the classical admittance depends on the RC time tau of the quantum dot, but the relevant time scale for the weak-localization correction and the admittance fluctuat ions is the dwell time. An extension of the circular ensemble is used for a statistical description of the energy dependence of the scatteri ng matrix.