Resonant inelastic x-ray scattering study of vector chiral ordered kagome antiferromagnet

We study the resonant inelastic x-ray scattering (RIXS) features of vector chiral ordered kagome antiferromagnets. Utilizing a group theoretical formalism that respects lattice site symmetry, we calculated the L-edge magnon contribution for the vesignieite compound BaCu3V2O8(OH)2. We show that polarization dependence of the L-edge RIXS spectrum can be used to track magnon branches. We predict a non-zero L-edge signal in the non-cross π−π polarization channel. At the K-edge, we derived the two-site effective RIXS and Raman scattering operator for two-magnon excitation in vesignieite using the Shastry–Shraiman formalism. Our derivation considers spin-orbit coupling effects in virtual hopping processes. We find vector chiral correlation (four-spin) contribution that is proportional to the RIXS spectrum. Our scattering operator formalism can be applied to a host of non-collinear non-coplanar magnetic materials at both the L and K-edge. We demonstrate that vector chiral correlations can be accessed by RIXS experiments.

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

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

Dirac Magnons and Topological Energy Gaps in Honeycomb Magnets

Fermionic Dirac particles have long been known to exist in electronic materials exhibiting linear dispersion relations within energy-momentum spectra, such as two-dimensional graphene. Recently, a bosonic version of Dirac particles was predicted to appear in the magnon excitation structures of honeycomb magnets. In this article, we review theoretical predictions of topological Dirac magnons in honeycomb ferromagnets, and their experimental observations using inelastic neutron scattering in Cr-based van der Waals materials.

Magnon and Phonon Excitations in Nanosized NiO

Single-crystal, microcrystalline and nanocrystalline nickel oxides (NiO) have been studied by Raman spectroscopy. A new band at ~200 cm−1 and TO-LO splitting of the band at 350–650 cm−1 have been found in the spectra of single-crystals NiO(100), NiO(110) and NiO(111). The Raman spectra of microcrystalline (1500 nm) and nanocrystalline (13–100 nm) NiO resemble those of the single crystals. They all contain the two-magnon band at 1500 cm−1, indicating that the oxides remain at room temperature in the antiferromagnetic phase. Besides, a new sharp Raman band has been observed at 500 cm−1 in nanocrystalline NiO. Its temperature dependence suggests the magnetic origin of the band, possibly associated with the one-phonon–one-magnon excitation at the Brillouin zone centre.