Flux Flow Noise and Dynamical Transitions in a Flux Line Lattice

Generation of low frequency broadband noise is studied in the low- $T_c$ superconductor 2 $H$- ${\mathrm{NbSe}}_2$ near the “peak effect.” A striking dependence on both current and magnetic field is observed in the power, spectral shape, and non-Gaussian nature of the noise. The noise is very large in the plastic flow regime of the dynamics, and small in both the elastic flow and fluid flow regimes. The results show a rapid decrease in the velocity correlation length, a measure of the spatial homogeneity of the moving flux line assembly, as the upper critical field is approached.