Specific heat and metal-insulator transition of (BEDT-TTF)2MZn(SCN)4(M=Cs,Rb)

We have studied thermal properties of (BEDT- TTF)2MZn (SCN)4(M=Cs, Rb) with special interest in the metal-insulator transition, which is drastically modified by the cooling condition, and mysterious low temperature electronic states, where 1H-NMR relaxation rate T1−1 and magnetic susceptibility exhibit an anomalous enhancement. At the transition (Tc=20K), we observed an abrupt jump of the specific heat and finite latent heat ΔQ for the CsZn salt. In the case of RbZn salt, it can be clarified that rapid cooling lead to the enhancements of γT term and peculiar lower temperature electronic states.