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arXiv:1006.5052 · Physical Review B

Bond-order wave phase, spin solitons, and thermodynamics of a frustrated linear spin- 1 2 Heisenberg antiferromagnet

Manoranjan Kumar, S. Ramasesha, Z. G. Soos

Published Feb 10, 2010• 35 citations
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Abstract

The linear spin-$\frac{1}{2}$ Heisenberg antiferromagnet with exchanges ${J}_{1}$ and ${J}_{2}$ between first and second neighbors has a bond-order wave (BOW) phase that starts at the fluid-dimer transition at ${J}_{2}/{J}_{1}=0.2411$ and is particularly simple at ${J}_{2}/{J}_{1}=1/2$. The BOW phase has a doubly degenerate singlet ground state, broken inversion symmetry, and a finite-energy gap ${E}_{m}$ to the lowest-triplet state. The interval $0.4<{J}_{2}/{J}_{1}<1.0$ has large ${E}_{m}$ and small finite-size corrections. Exact solutions are presented up to $N=28$ spins with either periodic or open boundary conditions and for thermodynamics up to $N=18$. The elementary excitations of the BOW phase with large ${E}_{m}$ are topological spin-$\frac{1}{2}$ solitons that separate BOWs with opposite phase in a regular array of spins. The molar spin susceptibility ${\ensuremath{\chi}}_{M}(T)$ is exponentially small for $T⪡{E}_{m}$ and increases nearly linearly with $T$ to a broad maximum. ${J}_{1}$ and ${J}_{2}$ spin chains approximate the magnetic properties of the BOW phase of Hubbard-type models and provide a starting point for modeling alkali-tetracyanoquinodimethane salts.

DOI
10.1103/physrevb.81.054413

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