ac electric and magnetic responses of nonconnected Aharonov-Bohm rings

Abstract

The signature of phase coherence on the electric and magnetic response of ${10}^{5}$ nonconnected Aharonov-Bohm rings is measured by a resonant method at 350 MHz between 20 mK and 500 mK. The rings are etched in a GaAs-${\mathrm{Al}}_{x}{\mathrm{Ga}}_{1\ensuremath{-}x}\mathrm{As}$ heterojunction. Both quantities exhibit an oscillating behavior with a periodicity consistent with half a flux quantum ${\ensuremath{\Phi}}_{0}/2=h/2e$ in a ring. We find that electric screening is enhanced when time-reversal symmetry is broken by magnetic field, leading to a positive magnetopolarizability, in agreement with theoretical predictions for isolated rings at finite frequency. Temperature and electronic-density dependences are investigated. The dissipative part of the electric response, the electric absorption, is also measured and leads to a negative magnetoconductance. The magnetic orbital response of the very same rings is also investigated. It is consistent with diamagnetic persistent currents of 0.25 nA. This magnetic response is an order of magnitude smaller than the electric one, in qualitative agreement with theoretical expectations.