Nesting instability in a family of α-(BEDT-TTF)2MHg(SCN)4 [M = K, Rb, NH4] studied by 13C-NMR

We have investigated low-temperature electronic states of the organic conductors, α-(BEDT-TTF)2MHg(SCN)4 [M = K, Rb and NH4] in terms of 13C-NMR and dc susceptibility measurements. For all the compounds, the overall temperature dependence of 1/(T1T) scales to that of χs2 except below the nesting instability. For M = Rb and K salts, the 1/(T1T) decreased below the transition temperatures without line-broadening or relaxation enhancement. The spectra changed from complicated lines to an apparently simple Pake doublet below the nesting temperatures. All of the NMR data are successfully explained by reduction of the electronic density-of states below the transition but do not have any sign of magnetic order.