Spin wave Hamiltonian and anomalous scattering in NiPS$_3$

Abstract

We report a comprehensive spin wave analysis of the semiconducting honeycomb van der Waal antiferromagnet NiPS3. Using single crystal inelastic neutron scattering, we map out the full Brillouin zone and fit the observed modes to a spin wave model with rigorously defined uncertainty. We find that the third neighbor exchange J3 dominates the Hamiltonian, a feature which we fully account for by ab-initio density functional theory calculations. We also quantify the degree to which the three-fold rotation symmetry is broken and account for the Q = 0 excitations observed in other measurements, yielding a spin exchange model which is consistent across multiple experimental probes. We also identify a strongly reduced static ordered moment and reduced low-energy intensity relative to the linear spin wave calculations, signaling unexplained features in the magnetism which requires going beyond the linear spin wave approximation.

Exciton-spin interactions in antiferromagnetic charge-transfer insulators

“…Similar arrangements of clusters are realized in the double perovskite structure (e.g., Sr 2 CuTeO 6 ) [28,29] and the crystal structure of Ba 3 CuSb 2 O 9 [30,31]. If the nearest-neighboring (NN) molecular orbitals are orthogonal, e.g., as in the edgeshared cuprates [32], a similar idea can be extended further to the spatially separated second or third NN clusters (as relevant for NiPS 3 [33]).…”

“…The vdW magnet NiPS 3 has the edge-shared octahedral structure, where the AFM spin-exchange interaction between the NN clusters is very weak because the p x and p y orbitals in the shared ligand site are nearly orthogonal [36]. Instead, the d-p-p-d network between the third-NNs gives the largest spin exchange in NiPS 3 [33,[36][37][38], implying that the interactions between two separated third-NN clusters are the most effective. Our theory shows a magnetic sideband structure near the excitonic peak as observed in NiPS 3 [14,18].…”

“…5). Similar cluster arrangements appear in realistic materials, e.g., in double perovskite magnets and in the second-or third-NN clusters when the NN orbitals are nearly orthogonal as in NiPS 3 [28,31,33]. The form of the Hamiltonian for the g sector Ĥ (12) eff;g is the same as Eq.…”