13C-NMR Study of Mott Insulating Phase in κ-(BEDT-TTF)2X Family

The κ-(BEDT-TTF)2X family are quite attractive in the study of metal-insulator transitions and competition between superconductivity and magnetic ordering. We report 13C-NMR study of X= Cu[N(CN)2]Cl salt and discuss on the electronic structure, compared with the results of superconducting salts. In addition, we found that the deuterated Cu[N(CN)2]Br salt, when cooled rapidly, showes AF ordering like the Cu[N(CN)2]Cl salt with only minor fraction of superconducting phase. We also report 13C-NMR study of this salt.