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Gapless Excitation above a Domain Wall Ground State in a Flat-Band Hubbard Model

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Abstract

We construct a set of exact ground states with a localized ferromagnetic domain wall and with an extended spiral structure in a deformed flat-band Hubbard model in arbitrary dimensions. We show the uniqueness of the ground state for the half-filled lowest band in a fixed magnetization subspace. The ground states with these structures are degenerate with all-spin-up or all-spin-down states under the open boundary condition. We represent a spin one-point function in terms of local electron number density, and find the domain wall structure in our model. We show the existence of gapless excitations above a domain wall ground state in dimensions higher than one. On the other hand, under the periodic boundary condition, the ground state is the all-spin-up or all-spin-down state. We show that the spin-wave excitation above the all-spin-up or -down state has an energy gap because of the anisotropy

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Authors and Affiliations

  1. Department of Physics, Science and Technology, Nihon University, Tokyo, Japan

    Makoto Homma & Chigak Itoi

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  1. Makoto Homma
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  2. Chigak Itoi
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Correspondence to Makoto Homma.

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Homma, M., Itoi, C. Gapless Excitation above a Domain Wall Ground State in a Flat-Band Hubbard Model. J Stat Phys 119, 391–425 (2005). https://doi.org/10.1007/s10955-004-2723-4

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  • DOI: https://doi.org/10.1007/s10955-004-2723-4

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