Solitons and polarons in a spin density wave chain

Vladimir N. Men'shov, Victor V. Tugushev, M. Avignon

Norikazu Tomita, Hideo Fukutome

We show in the Hartree-Fock approximation that electronic defects which are SDW-CDW domain walls exist in the one dimensional extended Hubbard model of half filling. In the vicinity of the SDW-CDW phase boundary, SDW and CDW polarons and charged solitons split into confined pairs of these defects. They become freely mobile along a chain on the phase boundary. They have ±1/4 spins and ±1/2 charges in an equidistant lattice and are called halfons. Halfon pairs can convert smoothly the SDW and CDW and can be major quantum fluctuations in the SDW-CDW phase 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 CDW via the MDW. We derive the counting rules to explain their fractional spins and charges.

H.-J. Mikeska, Seiji Miyashita, Gerald H. Ristow

Y. Anusooya, Swapan Kumar Pati, S. Ramasesha

The phase diagram of halogen-bridged mixed-valence metal complexes (MX) has been studied using a two-band extended Peierls-Hubbard model employing the recently developed density-matrix renormalization group method. We present the energies, charge- and spin-density distributions, bond orders, and charge-charge and spin-spin correlations, for the ground state, for different parameters of the model. The effects of bond alternation and site-diagonal distortion on the ground-state properties are considered in detail. We observe that the site-diagonal distortion plays a significant role in deciding the nature of the ground state of the system. We find that while the charge-density-wave (CDW) and bond-order-wave (BOW) phases can coexist, the CDW and SDW (spin-density-wave) phases are mutually exclusive in most cases. We have also studied the doped MX chains both with and without bond alternation and site-diagonal distortion in the CDW as well as SDW regimes. We find that the additional charges in the polarons and bipolarons for hole doping are confined to a few sites, in the presence of bond alternation and site-diagonal distortion. For electron doping, we find that the additional charge(s) is (are) smeared over the entire chain length, and although the energetics implies a disproportionation of the negatively charged bipolaron, the charge- and spin-density distributions do not reflect this. A positively charged bipolaron disproportionates into two polarons in the SDW region. There is also bond-order evidence for compression of the bond length for the positively charged polaronic and bipolaronic systems and an elongation of the bonds for systems with negatively charged polarons and bipolarons.

Н. К. Балабаев, Victor Dmitrievich Lakhno

Davide Fioretto, Rogier Vljim, Martin Ganahl +4 more