Probing $\alpha$-RuCl$_3$ Beyond Magnetic Order: Effects of Temperature and Magnetic Field

TL;DR

This study explores the finite temperature and magnetic field effects on the spin dynamics of $ ext{α-RuCl}_3$, revealing a transition from magnetic order to a quantum paramagnetic state with complex spectral redistributions.

Contribution

It provides a detailed theoretical analysis of the dynamical response of $ ext{α-RuCl}_3$ under finite temperature and magnetic field, extending understanding beyond magnetic order.

Findings

Suppression of zigzag magnetic order under magnetic field.

Emergence of a quantum paramagnetic state connected to full polarization.

Large spectral weight redistributions due to anisotropic frustration.

Abstract

Recent studies have brought $\alpha$-RuCl$_3$ to the forefront of experimental searches for materials realizing Kitaev spin-liquid physics. This material exhibits strongly anisotropic exchange interactions afforded by the spin-orbit coupling of the 4d Ru centers. We investigate the dynamical response at finite temperature and magnetic field for a realistic model of the magnetic interactions in $\alpha$-RuCl$_3$. These regimes are thought to host unconventional paramagnetic states that emerge from the suppression of magnetic order. Using exact diagonalization calculations of the quantum model complemented by semi-classical analysis, we find a very rich evolution of the spin dynamics as the applied field suppresses the zigzag order and stabilizes a quantum paramagnetic state that is adiabatically connected to the fully polarized state at high fields. At finite temperature, we observe large redistributions of spectral weight that can be attributed to the anisotropic frustration of the model. These results are compared to recent experiments, and provide a roadmap for further studies of these regimes.