Charge disproportionation with lattice distortion of α-(BEDT-TTF)2RbHg(SCN)4 observed by 13C-NMR

To explore the connection between α-(BEDT-TTF)2I3 and α-(BEDT-TTF)2MHg(SCN)4 (M = K, Rb, Tl and NH4) and to resolve the difference between band picture and charge fluctuation of α-(BEDT-TTF)2MHg(SCN)4, we utilized 13C-NMR to examine α-(BEDT-TTF)2RbHg(SCN)4 under the conditions with a large hyperfine coupling constant at each site. The temperature dependence of site susceptibility showed the development of spin disproportionation as observed in α-(BEDT-TTF)2I3. We found that the linewidth of the A site only increased as temperature decreased from 200 to 100 K, a change associated with the development of lattice modulation. These findings indicate that density-wave modulation occurs during charge disproportionation instability