ac Dynamics of a Pinned Flux-Line Lattice

W. Henderson and E. Y. Andrei
Department of Physics and Astronomy, Rutgers University, Piscataway, New Jersey 08855
M. J. Higgins and S. Bhattacharya
NEC Research Institute, 4 Independence Way, Princeton, New Jersey 08540

The surface impedance of 2H-NbSe2 in the mixed state was measured over the frequency range 103000 MHz in fields up to 2 T. A crossover between pinned and viscous flux-line dynamics is observed at a pinning frequency, wp. The measured wp is compared to that predicted by a single-particle "washboard potential" model of pinning. When the flux lattice is in an ordered state, wp is in good agreement with the model. However, when it is in a metastable disordered state, wp is nearly two orders of magnitude larger than expected, indicating the appearance of internal degrees of freedom and glassy dynamics.