Field-induced phase transitions of the Kitaev material $\alpha$-RuCl${}_3$ probed by thermal expansion and magnetostriction

Abstract

High-resolution thermal expansion and magnetostriction measurements were performed on single crystals of $\alpha$-RuCl${}_3$ in magnetic fields applied parallel to the Ru-Ru bonds. The length changes were measured in the direction perpendicular to the honeycomb planes. Our data show clear thermodynamic characteristics for the field-induced phase transition at the critical field ${\mu }_0{H}_{c1}=7.8(2)$ T where the antiferromagnetic zigzag order is suppressed. At higher fields, a kink in the magnetostriction coefficient signals an additional phase transition around ${\mu }_0{H}_{c2}\approx 11$ T. The extracted Grüneisen parameter shows typical hallmarks for quantum criticality near $H_{c1}$, but also displays anomalous behavior above $H_{c1}$. We compare our experimental data with linear spin-wave calculations employing a minimal Kitaev-Heisenberg model in the semiclassical limit. Most of the salient features are in agreement with each other, however, the peculiar features in the high-field region above $H_{c1}$ cannot be accounted for in our modelling and hence suggest a genuine quantum nature. We construct a phase diagram for $\alpha$-RuCl${}_3$ showing two low-temperature transitions induced by an in-plane field along the Ru-Ru bonds.

arXiv comment14 pages, 10 figures

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• Heisenberg-Kitaev model in a magnetic field: $1/S$ expansion
• Magnetoelastic coupling and effects of uniaxial strain in $\alpha$-RuCl${}_3$ from first principles
• Angle-dependent thermodynamics of $\alpha$-RuCl${}_3$
• Kitaev Quantum Spin Liquids
• Revealing the Phase Diagram of Kitaev Materials by Machine Learning: Cooperation and Competition between Spin Liquids
• Investigation of the magnetoelastic coupling anisotropy in the Kitaev material $\alpha$-RuCl${}_3$
• Susceptibility anisotropy and its disorder evolution in models for Kitaev materials
• Stacking faults in $\alpha$-RuCl${}_3$ revealed by local electric polarization
• Acoustic phonon dispersion of $\alpha$-RuCl${}_3$
• Neutron spectroscopy evidence for a possible magnetic-field-induced gapless quantum-spin-liquid phase in a Kitaev material $\alpha$-RuCl${}_3$
• Signatures of a Quantum Critical Endpoint in the Kitaev Candidate Na${}_2$Co${}_2$TeO${}_6$
• Intermediate field-induced phase of the honeycomb magnet BaCo${}_2$(AsO${}_4$)${}_2$
• Phonon Dynamics in the Chiral Kitaev Spin Liquid
• Magnetostriction of α-RuCl3 flakes in the zigzag phase
• Chiral excitations and the intermediate-field spin-liquid regime in the Kitaev magnet $\alpha$-RuCl${}_3$
• Dilution of the magnetic lattice in the Kitaev candidate $\alpha$-RuCl${}_3$ by Rh${}^{3+}$ doping
• Thermal decomposition of the Kitaev material $\alpha$-RuCl${}_3$ and its influence on low-temperature behavior
• Magnetostriction in the $J$-$K$-$\Gamma$ model: Application of the numerical linked cluster expansion
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