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arXiv:cond-mat/0101273 · Physical review. B, Condensed matter

Series study of the one-dimensional S−T spin-orbital model

Weihong Zheng, J. Oitmaa

Published Jun 11, 2001• 11 citations
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Abstract

We use perturbative series expansions about a staggered dimerized ground state to compute the ground-state energy, triplet excitation spectra, and spectral weight for a one-dimensional model in which each site has an $S=\frac{1}{2}$ spin ${\mathbf{S}}_{i}$ and a pseudospin ${\mathbf{T}}_{i},$ representing a doubly degenerate orbital. An explicit dimerization is introduced to allow the study of the confinement of spinon excitations. The elementary triplet represents a bound state of two spinons and is stable over much of the Brillouin zone. A special line is found in the gapped spin-liquid phase, on which the triplet excitation is dispersionless. The formation of triplet bound states is also investigated.

DOI
10.1103/physrevb.64.014410

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The infinite Heisenberg XXZ spin-12\frac{1}{2}21​ chain in the gapped antiferromagnetic regime has two degenerate vacua and kink topological excitations (which are also called spinons) interpolating between these vacua as elementary excitations. Application of an arbitrary weak staggered longitudinal magnetic field hhh induces a long-range attractive potential between two adjacent spinons leading to their confinement into ``meson'' bound states. Exploiting the integrability of the XXZ model in the deconfined phase h=0h=0h=0, we perform perturbative calculations of the energy spectra of the two-spinon bound states in the weak confinement regime at $h\ensuremath{\rightarrow}+0$, using the strength of the staggered magnetic field hhh as a small parameter. Both transverse and longitudinal dynamical structure factors of the local spin operators are calculated as well in the two-spinon approximation in the weak confinement regime to the leading order in hhh.
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