paper

Instabilities of the Hubbard chain in a magnetic field

arXiv:cond-mat/9701104 · doi:10.1103/PhysRevB.55.7565

Abstract

We find and characterize the instabilities of the repulsive Hubbard chain in a magnetic field by studing all response functions at low frequency ωand arbitrary momentum. The instabilities occur at momenta which are simple combinations of the (U=0) σ=\uparrow ,\downarrow Fermi points, \pm k_{Fσ}. For finite values of the on-site repulsion U the instabilities occur for single σelectron adding or removing at momenta \pm k_{Fσ}, for transverse spin-density wave (SDW) at momenta \pm 2k_F (where 2k_F=k_{F\uparrow}+k_{F\downarrow}), and for charge-density wave (CDW) and SDW at momenta \pm 2k_{F\uparrow} and \pm 2k_{F\downarrow}. While at zero magnetic field removing or adding single electrons is dominant, the presence of that field brings about a dominance for the transverse \pm 2k_F SDW over all the remaining instabilities for a large domain of and density n values. We go beyond conformal-field theory and study divergences which occur at finite frequency in the one-electron Green function at half filling and in the transverse-spin response function in the fully-polarized ferromagnetic phase.

LaTeX file, 15 pages plus 9 figures. Accepted for publication in Phys. Rev. B. The figures can be obtained upon request from Pedro Sacramento at [email protected]

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