  Significant changes of the relative permittivity of a silver film have been
detected using the surface plasmon resonance (SPR) method when a constant
electric field is applied to a MDM (metal-dielectric-metal) nanostructure. The
structure looks like a capacitor with a 177-nm dielectric corundum film placed
between two silver films 49nm and 37nm thick. The effect manifests itself as a
noticeable change of the reflectivity of the structure when the voltage of up
to 30V is applied to the electrodes. We have a good agreement between the
theory and experiment only if we suppose that the optical parameters of anode
and cathode silver films change differently and the Al_2O_3 film absorbs the
incident light. The refraction coefficient of the cathode silver layer is shown
to become zero when the applied voltage is above 16V.
