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

S. Gass; P. M. Cônsoli; V. Kocsis; L. T. Corredor; P. Lampen-Kelley; D. G. Mandrus; S. E. Nagler; L. Janssen; M. Vojta; B. Büchner; A. U. B. Wolter

doi:10.1103/physrevb.101.245158

arXiv · 2003.07081

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

S. Gass·P. M. Cônsoli·V. Kocsis·L. T. Corredor·P. Lampen-Kelley·D. G. Mandrus·S. E. Nagler·L. Janssen·M. Vojta·B. Büchner·A. U. B. Wolter

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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 $\mu_0H_{c1} = 7.8(2)$ T where the antiferromagnetic zigzag order is suppressed. At higher fields, a kink in the magnetostriction coefficient signals an additional phase transition around $\mu_0H_{c2} \approx 11$ T. The extracted Gr\"uneisen 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.

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S. Gass, P. M. Cônsoli, V. Kocsis, L. T. Corredor, P. Lampen-Kelley, D. G. Mandrus, S. E. Nagler, L. Janssen, M. Vojta, B. Büchner, A. U. B. Wolter. 2020-03-16. Field-induced phase transitions of the Kitaev material $\alpha$-RuCl$_3$ probed by thermal expansion and magnetostriction. https://doi.org/10.1103/physrevb.101.245158

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