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arXiv · 2507.17238

Coupling of magnetic and lattice collective excitations in the 2D van der Waals antiferromagnet FePS$_{3}$

Kartik Panda·Itzik Kapon·Dumitru Dumcenco·Dirk van der Marel·Alexey Kuzmenko·Nimrod Bachar
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Abstract

We combine polarized infrared magneto-transmission and Faraday angle rotation measurements to map the collective excitations of the van der Waals antiferromagnet FePS$_3$. Below the N\'{e}el temperature ($T_\mathrm{N} \approx 118~\mathrm{K}$), the phonon spectrum becomes strongly anisotropic, reflecting the underlying zigzag antiferromagnetic order. In contrast, a prominent excitation at $122~\mathrm{cm}^{-1}$ ($15$~meV) is polarization-independent, hardens on cooling, and splits linearly with magnetic field, identifying its magnetic origin. From absolute transmission and Faraday rotation, we reconstruct the circular optical conductivities and reveal a pronounced dichroism of the field-split excitations. The upper branch near $129~\mathrm{cm}^{-1}$ exhibits a reduced dichroic response, consistent with hybridization with a nearby infrared phonon. Several phonon modes exhibit sizable Faraday rotation, providing evidence for spin-phonon coupling and demonstrating that lattice vibrations acquire magnetic-field-dependent optical activity. In addition, additional excitations appear in the infrared spectra and a broad mid-infrared feature near $900~\mathrm{cm}^{-1}$ emerges only below $T_\mathrm{N}$, consistent with a modified lattice response in the magnetic state. These results highlight the anisotropic nature of spin--phonon coupling in FePS$_3$ and establish polarization-resolved magneto-optical spectroscopy as a powerful probe of coupled spin and lattice dynamics in two-dimensional antiferromagnets.

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Kartik Panda, Itzik Kapon, Dumitru Dumcenco, Dirk van der Marel, Alexey Kuzmenko, Nimrod Bachar. 2025-07-23. Coupling of magnetic and lattice collective excitations in the 2D van der Waals antiferromagnet FePS$_{3}$. https://doi.org/10.1103/fwb8-fwjb

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