Vortex structure and dynamics in -(ET) Cu(NCS)

We use Josephson plasma resonance (JPR) and DC torque magnetization measurements to investigate the vortex structure and dynamics in the layered organic superconductor -(ET) Cu(NCS) . JPR studies probe the AC response of this extreme type-II superconductor for currents driven along the low conductivity axis. An observed crossover in the magnetic "eld and temperature dependence of the JPR frequency, in close proximity to the irreversibility line, is attributed either to a melting or a depinning transition in the quasi-two-dimensional (Q2D) vortex structure. Angle and temperature dependent magnetization studies reveal the rich dynamical process by which magnetic #ux enters this highly anisotropic superconductor, as well as information on the structure of the vortices once inside. At extremely low temperatures (1(100mK), the sudden cessation of avalanching #ux jumps above an angleand temperature-dependent critical "eld B*( ,1), is indicative of Q2D vortex lattice melting. Thus, using these two very di!erent techniques, we are able to probe the vortex phase diagram over a wide temperature and magnetic "eld range. 2001 Elsevier Science B.V. All rights reserved.