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 Hc2-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 Tc in magnetic fields and then it reached T = 0 when H > HC2 in the end.