Transverse depinning and melting of a moving vortex lattice in driven periodic Josephson junction arrays

We study the effect of thermal fluctuations in a vortex lattice driven in t he periodic pinning of a Josephson junction array. The phase diagram curren t (I) vs temperature (T) is studied. Above the critical current I-c(T) we f ind a moving vortex lattice (MVL) with anisotropic Bragg peaks. For large c urrents I much greater than I-c(T), there is a melting transition of the MV L at T-M(I). When applying a small transverse current to the MVL, there is negligible dissipation at low T. We find an onset of transverse vortex moti on at a transverse depinning temperature T-tr(I) < T-M(I). [S0031-9007(99)0 9324-2].