Radio-frequency oscillations in two-dimensional superconducting In-InOx: Apossible evidence for vortex density waves

Large-amplitude radio-frequency oscillations were discovered in high sheet- resistance indium-indium-oxide films that carry nonuniform currents below t he zero-field superconducting transition. The sample geometry consists of a line that is oriented perpendicular to current flow inside a rectangular s ection of the film. As the de current increases above a threshold, the volt age spectrum displays several peaks which grow and shift toward higher freq uencies. The effect is attributed to wave excitations in the density of cur rent-depaired vortices and antivortices near the line tip.