1 6 M ay 2 00 1 Observation of the Fulde - Ferrell - Larkin - Ovchinnikov state in the quasi - two - dimensional organic superconductor κ - ( BEDT - TTF ) 2 Cu ( NCS

Observation of the Fulde-Ferrell-Larkin-Ovchinnikov state in the quasi-two-dimensional organic superconductor κ-(BEDT-TTF) 2 Cu(NCS) 2. Abstract Single crystals of the layered organic type II superconductor, κ-(BEDT-TTF) 2 Cu(NCS) 2 , have been studied in magnetic fields of up to 33 T and at temperatures between 0.5 K and 11 K using a compact differential suscep-tometer. When the magnetic field lies precisely in the quasi-two-dimensional planes of the material, there is strong evidence for a phase transition from the superconducting mixed state into a Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) state, manisfested as a change in the rigidity of the vortex system. The behaviour of the transition as a function of temperature is in good agreement with theoretical predictions. 1 state in superconductors subjected to high magnetic fields (for a summary, see Refs. 2,3 and references therein). In a metal in a magnetic field, the normal quasiparticles have separate 1