Field switching of superconductor-insulator bistability in artificially tuned organics

Layered organic superconductors situated in the vicinity of a superconductor-insulator (SI) phase boundary show switching between the SI bistable states by application of magnetic field. First, we show that an electronic phase of kappa-(BEDT-TTF)(2)[N(CN)(2)]Br [BEDT-TTF denotes bis(ethylenedithio)tetrathiafulvalene] can be finely tuned so as to approach the SI boundary by combination of chemical modification of the BEDT-TTF molecules and regulation of cooling rate. Then, we demonstrate that the superconducting phase tuned in this way undergoes a field-induced first-order transition into the insulating phase.