Dispersion of low-energy optical excitations in NiPS3 explained by singlet polaron theory
Abstract
Optical and resonant inelastic X-ray scattering (RIXS) experiments in the van der Waals antiferromagnet NiPS3 have revealed narrow excitonic resonances near 1.5 eV whose microscopic origin remains under debate. In this work we study the momentum dependence of these excitations using the singlet-polaron theory (SPT) previously developed for NiPS3. Within its framework, we calculate the spectral function of the corresponding effective model and extract the dispersion of the resulting quasiparticles. The theory naturally predicts two singlet excitations whose dynamics arise from their propagation in the zig-zag antiferromagnetic background (S=1) coupled to two-magnon processes. We show that the dispersion of the lowest-energy quasiparticle agrees very well with the excitonic dispersion measured by RIXS, reproducing both its overall shape and bandwidth along high-symmetry directions of the Brillouin zone. Our results provide a consistent interpretation of the optical excitations in terms of dispersive singlet polarons, and suggest that similar mechanisms may govern excitonic dynamics in other layered van der Waals antiferromagnets.
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BibTeX
@misc{hamad2026dispersion,
title = {{Dispersion of low-energy optical excitations in NiPS$_3$ explained by singlet polaron theory}},
author = {I. J. Hamad and C. S. Helman and A. E. Feiguin and L. O. Manuel and A. A. Aligia},
howpublished = {arXiv},
year = {2026},
month = oct,
doi = {10.48550/arxiv.2610.15230},
eprint = {2610.15230},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2610.15230},
note = {CC BY 4.0},
}
RIS
TY - UNPB
TI - Dispersion of low-energy optical excitations in NiPS_3 explained by singlet polaron theory
AU - I. J. Hamad
AU - C. S. Helman
AU - A. E. Feiguin
AU - L. O. Manuel
AU - A. A. Aligia
PY - 2026
DA - 2026/10/10
PB - arXiv
DO - 10.48550/arxiv.2610.15230
UR - https://arxiv.org/abs/2610.15230
AB - Optical and resonant inelastic X-ray scattering (RIXS) experiments in the van der Waals antiferromagnet NiPS_3 have revealed narrow excitonic resonances near 1.5 eV whose microscopic origin remains under debate. In this work we study the momentum dependence of these excitations using the singlet-polaron theory (SPT) previously developed for NiPS_3. Within its framework, we calculate the spectral function of the corresponding effective model and extract the dispersion of the resulting quasiparticles. The theory naturally predicts two singlet excitations whose dynamics arise from their propagation in the zig-zag antiferromagnetic background (S=1) coupled to two-magnon processes. We show that the dispersion of the lowest-energy quasiparticle agrees very well with the excitonic dispersion measured by RIXS, reproducing both its overall shape and bandwidth along high-symmetry directions of the Brillouin zone. Our results provide a consistent interpretation of the optical excitations in terms of dispersive singlet polarons, and suggest that similar mechanisms may govern excitonic dynamics in other layered van der Waals antiferromagnets.
ER -