Dynamic response of isolated Aharonov-Bohm rings coupled to an electromagnetic resonator
We have measured the flux dependence of both real and imaginary conductance of $GaAs/GaAlAs$ isolated mesoscopic rings at 310 MHz. The rings are coupled to a highly sensitive electromagnetic superconducting micro-resonator and lead to a perturbation of the resonance frequency and quality factor. This experiment provides a new tool for the investigation of the conductance of mesoscopic systems without any connection to invasive probes. It can be compared with recent theoretical predictions emphasizing the differences between isolated and connected geometries and the relation between ac conductance and persistent currents. We observe $Φ_0/2$ periodic oscillations on both components of the magnetoconductance. The oscillations of the imaginary conductance whose sign corresponds to diamagnetism in zero field, are 3 times larger than the Drude conductance $G_0$. The real part of the periodic magnetoconductance is of the order of $0.2 G_0$ and is apparently negative in low field. It is thus notably different from the weak localisation oscillations observed in connected rings, which are much smaller and opposite in sign.