ELEMENTARY DEFECTS, HALFONS, CONNECTING THE SDW AND CDW IN THE ONE-DIMENSIONAL EXTENDED HUBBARD-MODEL

We show in the Hartree-Fock approximation that electronic defects whic h are SDW-CDW domain walls exist in the one dimensional extended Hubba rd model of half filling. In the vicinity of the SDW-CDW phase boundar y, SDW and CDW polarons and charged solitons split into confined pairs of these defects. They become freely mobile along a chain on the phas e boundary. They have +/- 1/4 spins and +/- 1/2 charges in an equidist ant lattice and are called halfons. Halfon pairs can convert smoothly the SDW and CDW and can be major quantum fluctuations in the SDW-CDW p hase transition. In a bond alternated lattice their spins and charges, respectively, deviate from 1/4 and 1/2. On the SDW-CDW phase boundary , there exist new density waves called the mixed density waves (MDW). Halfons are classified by their trajectories connecting the SDW and CD W via the MDW. We derive the counting rules to explain their fractiona l spins and charges.