  The effect of the electromagnetic irradiation on the current-voltage
characteristics (IVCs) of a wide superconducting film is experimentally
investigated. In contrast to the microwave field (several GHz) which suppresses
vortex resistivity, the action of the rf field (tens of MHz) leads to
significant expansion of the linear part of the IVC due to rapid suppression of
the critical current with a slower change in the upper stability limit of the
vortex state where the phase-slip lines (PSLs) occur. With an increase in the
rf power, the stepwise structure of the IVC associated with the PSLs becomes
smoothed and eventually disappears. A model of the IVC in the adiabatic regime
is proposed, which explains the effects of smoothing of the voltage steps and
the suppression of the critical current.
