The critical state in κ-(BEDT-TTF)2Cu(NCS)2

Angle-dependent torque magnetization measurements, in the temperature range 25–200 mK, are used to investigate the rich dynamical process by which magnetic flux penetrates the mixed state of the extreme type-II organic superconductor κ-(BEDT-TTF)2Cu(NCS)2. Magneto-thermal instabilities are observed in the form of dramatic flux jumps. Our previous work [M. Mola et al., Phys. Rev. Lett. 86 (2001) 2130] has shown that the cessation of these flux jumps is associated with a melting transition from a two-dimensional vortex solid phase to a liquid state. In this study, we analyze the field and temperature dependence of the flux jumps themselves, thus providing access to considerable information concerning dissipation and the collective behavior of vortices within the mixed state of the title compound.