Competition between Mott transition and superconductivity under magnetic fields in strongly correlated organic superconductor κ-(BEDT-TTF) ₂Cu[N(CN)₂]Br

The phase diagram under magnetic fields in the organic Mott system κ-(BEDT-TTF)₂Cu[N(CN)₂]Br in which the bandwidth was tuned by the substitution of deuterated molecules was studied by means of the resistivity measurements. The lower critical point of the first-order Mott transition, which ended on the upper critical field _{H c2}-temperature plane of the superconductivity, was found in addition to the previously observed upper critical end point. The lower critical end point moved to a lower temperature together with the suppression of T _c in magnetic fields and then it reached T 0 when H > H _C2 in the end.