Measurement of Aharonov-Bohm oscillations in mesoscopic metallic rings in the presence of high-frequency electromagnetic fields

We report measurements of Aharonov-Bohm oscillations in normal metal rings in the presence of high frequency electromagnetic fields. The power dependence of the decoherence time scale tau_phi(P) agrees well with the anticipated power law tau_phi proportional to P^(-1/5) when the field-induced decoherence rate tau_ac^(-1) is large compared to the intrinsic decoherence rate tau_o^(-1), measured in the absence of external fields. As theoretically expected, we observe a decline in field-induced decoherence when tau_ac^(-1)<=tau_o^(-1). The frequency dependence of tau_phi shows a minimum in the oscillation amplitude at a characteristic frequency, omega_(ac)=1/tau_(o), where tau_(o) is evaluated from the oscillation amplitude using the standard mesoscopic theory. Both the suppression in the oscillation amplitude and the concomitant change in conductivity allow a direct measurement of the intrinsic decoherence time scale.