Magnetic Torque Studies On Fflo Phase In Magnetic-Field-Induced Organic Superconductor Lambda-(Bets)(2)Fecl4

Magnetic torque measurements have been carried out for two-dimensional magnetic-field-induced organic superconductor lambda-(BETS)(2)FeCl4, where BETS stands for bis(ethylenedithio) tetraselenafulvalene, to investigate the Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) phase. The in-plane upper critical field of the field-induced-superconducting phase steeply decreases with decreasing temperature below 2.2 K. The in-plane field dependence of the diamagnetic susceptibility shows a significant decrease below 25 T at low temperatures, showing that magnetic fluxes are less excluded from the sample. These results show the presence of the FFLO phase with the tricritical point between the FFLO, homogeneous superconducting, and paramagnetic metallic phases at 2.2 K and 23 T. The stability of the FFLO phase is also investigated as a function of the magnetic field angle and compared with theories.