Abstract
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.Graphical abstract
Highlights
Later on it was found that flat-band physics and corresponding localized multi-magnon states can appear in frustrated magnets at zero magnetic field in case that ferro- and antiferromagnetic interactions compete [16]
We examine the spin-1/2 XXZ0 sawtooth-chain model [25] focusing on the specific flatband features, i.e., localized-magnon properties
We present full exact diagonalization (ED) and finite-temperature Lanczos (FTL) data for the considered sawtooth-chain models of finite size N
Summary
Later on it was found that flat-band physics and corresponding localized multi-magnon states can appear in frustrated magnets at zero magnetic field in case that ferro- and antiferromagnetic interactions compete [16]. Very recently, using the three-coloring description Changlani et al [25,26] have noticed that the groundstate manifold of the spin-1/2 XXZ sawtooth chain with antiferromagnetic bonds J1 = J2 > 0 and with a negative zz anisotropy parameter ∆ = −1/2 (denoted as XXZ0 model) exhibits a huge degeneracy. As already noticed before (but not investigated) in reference [19], the XXZ0 sawtooth chain belongs to the class of flat-band systems hosting localized multi-magnon states in zero magnetic field. The three-coloring description of spin systems is a general and promising approach to
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