High-angular momentum excitations in collinear antiferromagnet FePS$_3$

TL;DR

This study investigates a unique high-angular momentum magnon excitation in FePS$_3$, revealing a four-times larger Zeeman splitting and proposing it as a multipolar magnon, suggesting potential for exotic magnetic states.

Contribution

The paper identifies and characterizes a novel $|S_z|=4$ multipolar magnon in FePS$_3$, highlighting its unusual Zeeman response and implications for exotic magnetic states.

Findings

Discovery of a four-times larger Zeeman splitting in FePS$_3$

Identification of a $|S_z|=4$ multipolar magnon

Implication of multipolar magnon condensation for exotic states

Abstract

We report on magneto-optical studies of the quasi-two-dimensional van der Waals antiferromagnet FePS$_3$. Our measurements reveal an excitation that closely resembles the antiferromagnetic resonance mode typical of easy-axis antiferromagnets, nevertheless, it displays an unusual, four-times larger Zeeman splitting in an applied magnetic field. We identify this excitation with an $|S_z|=4$ multipolar magnon -- a single-ion 4-magnon bound state -- that corresponds to a full reversal of a single magnetic moment of the Fe$^{2+}$ ion. We argue that condensation of multipolar magnons in large-spin materials with a strong magnetic anisotropy can produce new exotic states.