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arXiv · 2004.14730

Flat-band physics in the spin-1/2 sawtooth chain

Oleg Derzhko·Jürgen Schnack·D. V. Dmitriev·V. Ya. Krivnov·Johannes Richter
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Abstract

We consider the strongly anisotropic spin-1/2 $XXZ$ model on the sawtooth-chain lattice with ferromagnetic longitudinal interaction $J^{zz}=\Delta J$ and aniferromagnetic transversal interaction $J^{xx}=J^{yy}=J>0$. At $\Delta=-1/2$ the lowest one-magnon excitation band is dispersionless (flat) leading to a massively degenerate set of ground states. Interestingly, this model admits a three-coloring representation of the ground-state manifold [H.~J.~Changlani et at., Phys. Rev. Lett. {\bf 120}, 117202 (2018)]. We characterize this ground-state manifold and elaborate the low-temperature thermodynamics of the system. We illustrate the manifestation of the flat-band physics of the anisotropic model by comparison with two isotropic flat-band Heisenberg sawtooth chains. Our analytical consideration is complemented by exact diagonalization and finite-temperature Lanczos method calculations.

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Oleg Derzhko, Jürgen Schnack, D. V. Dmitriev, V. Ya. Krivnov, Johannes Richter. 2020-04-30. Flat-band physics in the spin-1/2 sawtooth chain. https://doi.org/10.1140/epjb/e2020-10224-1

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