Identification of Magnetic Interactions and High-field Quantum Spin Liquid in $\alpha$-RuCl$_3$

TL;DR

This study models the complex magnetic interactions in $ ext{RuCl}_3$, revealing a field-induced quantum spin liquid state and reconciling various experimental observations through advanced many-body simulations.

Contribution

It provides a comprehensive microscopic spin model for $ ext{RuCl}_3$ that explains its magnetic phases and field-induced quantum spin liquid, advancing understanding of Kitaev physics.

Findings

In-plane field causes polarization at ~7 T.

Out-of-plane field suppresses zigzag order at 35 T.

A gapless quantum spin liquid emerges above 35 T.

Abstract

The frustrated magnet $\alpha$-RuCl$_3$ constitutes a fascinating quantum material platform that harbors the intriguing Kitaev physics. However, a consensus on its intricate spin interactions and field-induced quantum phases has not been reached yet. Here we exploit multiple state-of-the-art many-body methods and determine the microscopic spin model that quantitatively explains major observations in $\alpha$-RuCl$_3$, including the zigzag order, double-peak specific heat, magnetic anisotropy, and the characteristic M-star dynamical spin structure, etc. According to our model simulations, the in-plane field drives the system into the polarized phase at about 7 T and a thermal fractionalization occurs at finite temperature, reconciling observations in different experiments. Under out-of-plane fields, the zigzag order is suppressed at 35 T, above which, and below a polarization field of 100 T level, there emerges a field-induced quantum spin liquid. The fractional entropy and algebraic low-temperature specific heat unveil the nature of a gapless spin liquid, which can be explored in high-field measurements on $\alpha$-RuCl$_3$.