Nature of Magnetic Excitations in the High-Field Phase of $\alpha$-RuCl$_3$

TL;DR

This study uses ESR to explore high-field spin dynamics in $ ext{α-RuCl}_3$, revealing magnon-based excitations and their behavior near critical magnetic fields, advancing understanding of its magnetic properties.

Contribution

The paper provides a detailed ESR analysis of $ ext{α-RuCl}_3$ in high magnetic fields, identifying excitation modes and their relation to other scattering data, highlighting magnon processes.

Findings

Identification of multiple ESR modes in high magnetic fields.

Dominance of single- and two-particle magnon processes beyond magnetic order boundary.

Discussion of excitation spectrum features near critical magnetic fields.

Abstract

We present comprehensive electron spin resonance (ESR) studies of in-plane oriented single crystals of $\alpha$-RuCl$_3$, a quasi-two-dimensional material with honeycomb structure, focusing on its high-field spin dynamics. The measurements were performed in magnetic fields up to 16 T, applied along the [110] and [100] directions. Several ESR modes were detected. Combining our findings with recent inelastic neutron- and Raman-scattering data, we identify most of the observed excitations. Most importantly, we show that the low-temperature ESR response beyond the boundary of the magnetically ordered region is dominated by single- and two-particle processes with magnons as elementary excitations. The peculiarities of the excitation spectrum in the vicinity of the critical field are discussed.