Nonequilibrium vortex-density-wave state in two-dimensional superconductors

A numerical study of nonuniform current flow in a two-dimensional supercond uctor suggests that current-depaired vortices and antivortices can form a s table nonequilibrium vortex-density-wave state. A necessary condition for g enerating vortex density waves is a de current distribution that displays a pronounced symmetrical dip along the direction of equipotential lines. Whe n the depth of the current density profile exceeds a crossover depth, the s tationary densities of vortices and antivoaices evolve into two coupled den sity waves which travel in opposite directions. For relatively deep current profiles, the density waves produce local-density oscillations whose frequ ency increases linearly with increasing current profile depth. A dip in the current density profile can be induced in two-dimensional superconducting In-InOx films that use a special geometry of long-line inhomogeneities. As the de current increases above a threshold, the measured voltage spectra di splay peaks which grow and shift toward higher radio frequencies. The detec ted spectral peaks, whose frequency increases linearly with current, result from the periodic motion of current-depaired vortex density waves. [S0163- 1829(99)06329-8].