  We have investigated a mesoscopic photovoltaic (PV) effect in micron-size Au
rings in which a dc voltage Vdc is generated in response to microwave
radiation. The effect is due to the lack of inversion symmetry in a disordered
system. Aharonov-Bohm PV oscillations with flux period h/e have been observed
at low microwave intensities for temperatures ranging from 1.4 to 13 K. For
moderate microwave intensities the h/e PV oscillations are completely quenched
providing evidence that the microwaves act to randomize the phase of the
electrons. Studies of the temperature dependence of Vdc also provide evidence
of the dephasing nature of the microwave field. A complete theoretical
explanation of the observed behavior seems to require a theory for the PV
effect in a ring geometry.
