Centipede ladder at quarter filling

Details Centipede ladder at quarter filling Centipede ladder at quarter filling

2007-02-13

arxiv.org/abs/cond-mat/0702307v1

Phys. Rev. B75, 224405 (2007)

Physics

Condensed Matter

Strongly Correlated Electrons

10 pages, 7 eps figures

Scientific paper

10.1103/PhysRevB.75.224405

We study the ground state and excitation spectrum of a quasi one-dimensional nanostructure consisting of a pole and rungs oriented in the opposite directions ("centipede ladder", CL) at quarter filling. The spin and charge excitation spectra are found in the limits of small and large longitudinal hopping $t_\|$ compared to the on-rung hopping rate $t_\perp$ and exchange coupling $I_\perp$. At small $t_\|$ the system with ferromagnetic on-rung exchange demonstrates instability against dimerization. Coherent propagation of charge transfer excitons is possible in this limit. At large $t_\|$ CL behaves like two-orbital Hubbard chain, but the gap opens in the charge excitation spectrum thus reducing the symmetry from SU(4) to SU(2). The spin excitations are always gapless and their dispersion changes from quadratic magnon-like for ferromagnetic on-rung exchange to linear spinon-like for antiferromagnetic on-rung exchange in weak longitudinal hopping limit.

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