Specific heat study of α-(BEDT-TTF)2MHg(SCN)4

The low-temperature specific heat of α-phase of (BEDT-TTF)2MHg(SCN)4 (M=K, Rb, NH4), where BEDT-TTF is bis- (etylenedithio) tetrathiafulvalene, is studied. The electronic specific heat coefficient (γ) estimated from the data between 1K and 2.3K amounts to 5.3, 10.3, 28.8mJ/mol K2 for M=K, Rb and NH4, respectively. The K-salt does not have distinct anomally around 8K within the precision of our experiments, implying that the transition occurs with a gradual change of electronic structure.