Mott transition and superconductivity in the strongly correlated organic superconductor κ- (BEDT-TTF)2 Cu [N (CN)2] Br

The magnetic-field effect on the phase diagram of the organic Mott system κ- (BEDT-TTF)2 Cu [N (CN)2] Br in which the bandwidth was tuned by the substitution of deuterated molecules was studied by means of the resistivity measurements performed in magnetic fields. The lower critical point of the first-order Mott transition, which ended on the upper critical field Hc2 -temperature plane of the superconductivity, was determined experimentally in addition to the previously observed upper critical end point. The lower critical end point moved to a lower temperature with the suppression of Tc in magnetic fields and the Mott transition recognized so far as the S-shaped curve reached T=0 when H> Hc2 in the end.