  We report a novel insulator-insulator transition arising from the internal
charge degrees of freedom in the two-dimensional quarter-filled organic salt
beta-(meso-DMBEDT-TTF)2PF6. The optical conductivity spectra above Tc = 70 K
display a prominent feature of the dimer-Mott insulator, characterized by a
substantial growth of a dimer peak near 0.6 eV with decreasing temperature. The
dimer-peak growth is rapidly quenched as soon as a peak of the charge order
shows up below Tc, indicating a competition between the two insulating phases.
Our infrared imaging spectroscopy has further revealed a spatially competitive
electronic phases far below Tc, suggesting a nature of quantum phase transition
driven by material-parameter variations.
