MICROWAVE-INDUCED OSCILLATIONS IN THE CONDUCTANCE OF A MESOSCOPIC RING

We calculate the conductance of a mesoscopic ring subject to a pumping microwave field. We find that the electromagnetic field has the same effect as a superlattice structure, deforming the electronic energy spectrum of the ring into minibands. The shape of the spectrum depends crucially on the intensity of the pumping. Due to the induced miniband structure the character of the quantum oscillations of the ring conductance - Aharonov-Bohm (AB) effect - varies drastically with the amplitude of the microwave field. This is because the position of the minibands can be shifted relative to the Fermi energy by varying the field amplitude. When the Fermi level moves from a position within a miniband to a forbidden gap, the AB oscillations changes from having a metallic to a dielectric character. In the vicinity of the forbidden bands, corresponding to Bragg reflection, a new resonant tunneling channel for transport through the ring appears. We calculate the position and lineshape of the resonant conductance peaks as a function of magnetic flux and intensity of the pumping field.