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arXiv:2207.12708 · Physical review. B./Physical review. B

Dynamics of spin- 12 J1–J2 model on the triangular lattice

A. V. Syromyatnikov

Published Nov 17, 2022• 3 citations
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Abstract

We discuss the spin-$\frac{1}{2}\phantom{\rule{4pt}{0ex}}{J}_{1}--{J}_{2}$ model on the triangular lattice using recently proposed bond-operator theory (BOT). In agreement with previous discussions of this system, we obtain four phases upon ${J}_{2}$ increasing: the phase with ${120}^{\ensuremath{\circ}}$ ordering of three sublattices, the spin-liquid phase, the state with the collinear stripe order, and the spiral phase. The ${120}^{\ensuremath{\circ}}$ and the stripe phases are discussed in detail. All calculated static characteristics of the model are in good agreement with previous numerical findings. In the ${120}^{\ensuremath{\circ}}$ phase, we observe the evolution of the quasiparticles' spectra and dynamical structure factors (DSFs) upon approaching the spin-liquid phase. Some of the considered elementary excitations were introduced first in our recent study of this system at ${J}_{2}=0$ using the BOT. In the stripe phase, we observe that the doubly degenerate magnon spectrum known from the spin-wave theory (SWT) is split by quantum fluctuations, which are taken into account more accurately in the BOT. As compared with other known findings of the SWT in the stripe state, we observe additional spin-1 and spin-0 quasiparticles which give visible anomalies in the transverse and longitudinal DSFs. We obtain also a special spin-0 quasiparticle named the singlon that produces a peak only in the four-spin correlator and which is invisible in the longitudinal DSF. We show that the singlon spectrum lies below energies of all spin-0 and spin-1 excitations in some parts of the Brillouin zone. The singlon spectrum at zero momentum can be probed by the Raman scattering.

DOI
10.1103/physrevb.106.184415

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A key feature of the newly discovered altermagnet is that its spin degeneracy is lifted, although it has an antiferromagnetic order and zero net magnetization. In this work, we investigate a frustrated spin-1/2 J1J_1J1​-J2J_2J2​-δδδ Heisenberg model on the square lattice by the tensor network methodin combination with the linear spin-wave theory, with our focus on both the magnon excitations and longitudinal excitations.For a small J2J_2J2​ and a finite range of δδδ we demonstrate that such a model hosts an altermagnetic ground state. Its magnon spectrum is split into two branches and the largest splitting occurs at (±π/2,±π/2)\left(\pmπ/2, \pmπ/2\right)(±π/2,±π/2) in the Brillouin zone. The magnitudes of splitting in the two magnon modes are equal with respect to the case of δ=0δ=0δ=0. Dynamical spin structure factors show that the low-energy peak in the longitudinal spectral weight around (π/2,π/2)(π/2, π/2)(π/2,π/2) is also split, and thus the relative positions of the magnon modes and longitudinal modes in energy may change in the presence of a finite δδδ. These findings demonstrate that the altermagnets harbor more complex quantum dynamics than the conventional collinear antiferromagnets.