Cooperative effects of electron correlation and charge ordering on the metal-insulator transition in quasi-one-dimensional deuteratedCu

We study the changes in the electronic structure of a quasi-one-dimensional organic conductor, deuterated (Formula presented)Cu, across the CDW/M-I (charge-density-wave/metal-insulator) transition at (Formula presented) K, using temperature-dependent (30-300 K) high-resolution photoemission spectroscopy. Above the mean-field (MF) transition temperature ((Formula presented)), the system shows typical metallic behavior with small but finite density of states at (Formula presented). The spectral weight in the vicinity of (Formula presented) decreases systematically upon decreasing temperature below (Formula presented) even in the metallic phase, resulting in a pseudogap formation above (Formula presented). This behavior continues across (Formula presented) and causes the M-I transition. The spectral weight is transferred to energies much larger than the gap, indicating a cooperative effect of strong electron correlation and structural changes which imply decreases in interchain coupling across the M-I transition.