Observation of the Fulde-Ferrell-Larkin-Ovchinnikov state in the quasi-two-dimensional organic superconductor κ-(BEDT-TTF)₂Cu(NCS)₂(BEDT-TTF=bis(ethylene-dithio)tetrathiafulvalene)

Abstract

Single crystals of the layered organic type II superconductor,\n$\\kappa$-(BEDT-TTF)$_{2}$Cu(NCS)$_{2}$, have been studied in magnetic fields of\nup to 33 T and at temperatures between 0.5 K and 11 K using a compact\ndifferential susceptometer. When the magnetic field lies precisely in the\nquasi-two-dimensional planes of the material, there is strong evidence for a\nphase transition from the superconducting mixed state into a\nFulde-Ferrell-Larkin-Ovchinnikov (FFLO) state, manisfested as a change in the\nrigidity of the vortex system. The behaviour of the transition as a function of\ntemperature is in good agreement with theoretical predictions.\n