  A two dimensional electron system without spatial inversion symmetry develops
a sample specific dc voltage when exposed to a microwave radiation at low
temperature. We investigate this photovoltaic (PV) effect, in the case where
spatial symmetry is broken by an evanescent high-frequency potential. We
measure the induced PV voltage in a ${\rm GaAs/Ga_{1-x}Al_{x}As}$ Hall bar at
magnetic fields in the Tesla range. We find that in this regime the induced PV
voltage is anti-symmetric with magnetic field, and exhibits regular
Shubnikov-de Haas like oscillations. Our experimental results can be understood
from a simple model, which describes the effect of stationary orbital currents
caused by microwave driving.
