Methyl Rotation and Reentrant Metal-Insulator Transition in Deuterated (DMe-DCNQ1) 2 Cu System

We studied the thermal property of metal complex salts (DMe-DCNQI) 2 Cu formed of DMe-DCNQI molecules of which some of hydrogen atoms are substituted by deuterium atoms. In those systems, we have discovered peaks in the specific heat originating from the orientation freedom of deuterated methyl groups. In systems containing methyl groups with one deuterium atom (CH 2 D), we found Schottky type of specific heat. In system with CHD 2 , we observed peaks not of Schottky type. To find out the origin and mechanism of these anomalies, we carried out the thermal study of the mixed crystals composed of molecules with CH 2 D and those with CHD 2 . We clarified the conformational ordering of CHD 2 molecular along c axis in the DCNQI-Cu system. Methyl Rotation Thermal properties Order-disorder transition M-I transition Phase Transition Mott Transition CDW Specific heat Deuteration