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

Abstract

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 ${\ensuremath{\tau}}_{\ensuremath{\phi}}(P)$ agrees well with the anticipated power law ${\ensuremath{\tau}}_{\ensuremath{\phi}}\ensuremath{\propto}{P}^{\ensuremath{-}1∕5}$ when the field-induced decoherence rate ${\ensuremath{\tau}}_{\mathit{ac}}^{\ensuremath{-}1}$ is large compared to the intrinsic decoherence rate ${\ensuremath{\tau}}_{o}^{\ensuremath{-}1}$, measured in the absence of external fields. As theoretically expected, we observe a decline in field-induced decoherence when ${\ensuremath{\tau}}_{\mathit{ac}}^{\ensuremath{-}1}\ensuremath{\leqslant}{\ensuremath{\tau}}_{o}^{\ensuremath{-}1}$. The frequency dependence of ${\ensuremath{\tau}}_{\ensuremath{\phi}}$ shows a minimum in the oscillation amplitude at a characteristic frequency ${\ensuremath{\omega}}_{\mathit{ac}}\ensuremath{\simeq}1∕{\ensuremath{\tau}}_{o}$, where ${\ensuremath{\tau}}_{o}$ 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.