  We investigate the current-phase-relation (CPR) of long diffusive
superconductor-normal metal-superconductor (SNS) Josephson junctions in
thermodynamic equilibrium and under microwave irradiation. While in equilibrium
good agreement with the predictions of quasi-classical theory is found, we
observe that the shape of the CPR can be strongly affected by microwave
irradiation. Close to a Josephson-phase difference of pi, the supercurrent can
be strongly suppressed when increasing the rf-power. Our results can be
understood in terms of microwave excitation of low-lying Andreev bound states
across the mini-gap in the junction. In the frequency interval studied, this
mechanism becomes important when the mini-gap closes at a phase difference of
pi.
