Flat-band physics in the spin-1/2 sawtooth chain
Institute for Condensed Matter Physics, National Academy of Sciences of Ukraine,
Svientsitskii Street 1,
2 Max-Planck-Institut für Physik komplexer Systeme, Nöthnitzer Straße 38, 01187 Dresden, Germany
3 Fakultät für Physik, Universität Bielefeld, Postfach 100131, 33501 Bielefeld, Germany
4 Institute of Biochemical Physics of RAS, Kosygin Street 4, 119334 Moscow, Russia
5 Institut für Physik, Otto-von-Guericke-Universität Magdeburg, P.O. Box 4120, 39016 Magdeburg, Germany
a e-mail: firstname.lastname@example.org
Received in final form: 5 July 2020
Published online: 24 August 2020
We consider the strongly anisotropic spin-1/2 XXZ model on the sawtooth-chain lattice with ferromagnetic longitudinal interaction Jzz = ΔJ and aniferromagnetic transversal interaction Jxx = Jyy = J > 0. At Δ = −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 al., Phys. Rev. Lett. 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.
Key words: Solid State and Materials
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