METAL-INSULATOR-TRANSITION IN DOPED CONDUCTING POLYMERS - DISAPPEARANCE OF ELECTRONIC GAP WITH PERSISTING BOND ALTERNATION

Electronic states are investigated in doped trans-polyacetylene, using the SSH model with site-type impurities randomly distributed. Each impurity accepts one electron. Lattice configuration and electronic wave functions are determined self-consistently with full lattice relaxation. The order parameter remains larger than that by Mele and Rice, as the disorder intensifies. The energy gap vanishes when the concentration is several percent and a gapless Peierls state takes place. The present results well explain the appearance of the metallic Pauli susceptibility, its magnitude, and the critical concentration, characteristic to the metal-insulator transition observed in experiments. The persistence of dimerization is also consistent with the X-ray studies. The wave function tends to extend more easily than Su's estimations.