Melting of flux lines in an alternating parallel current

We use a Langevin equation to examine the dynamics and fluctuations of a fl ux line (FL) in the presence of an alternating longitudinal current J(paral lel to)(omega) The magnus and dissipative forces are equated to those resul ting from line tension, confinement in a harmonic cage by neighboring FLs, parallel current, and noise. The resulting mean-square FL fluctuations are calculated exactly, and a Lindemann criterion is then used to obtain a none quilibrium "phase diagram" as a function of the magnitude and frequency of J(parallel to)(omega) For zero frequency, the melting temperature of the mi xed phase (a lattice, or the putative "Bose" or "Bragg glass") vanishes at a limiting current. However, for any finite frequency, there is a nonzero m elting temperature. [S0163-1829(99)06709-0].