Anomalous low-temperature properties of the degenerate one-dimensional Hubbard model

Unusual properties of the Hubbard chain of arbitrary degeneracy N and excluded-site occupations of more than two electrons are presented: (i) In zero field and in the limit of large N the ground state resembles an interacting Bose gas. The 1/N contributions vanish identically, so that corrections to leading order are 1/${\mathrm{N}}^2$. (ii) The susceptibility at T=0 shows logarithmic singularities as H→0. (iii) The Hubbard model and the Heisenberg chain have the same low-energy spin excitations for all U. (iv) The specific-heat coefficient γ is singular. These properties hold for arbitrary band filling and (ii)–(iv) hold for all N≥2.