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arXiv · 1912.11058

Orientation Dependence of the Magnetic Phase Diagram of Yb$_2$Ti$_2$O$_7$

S. Säubert·A. Scheie·C. Duvinage·J. Kindervater·S. Zhang·H. J. Changlani·Guangyong Xu·S. M. Koohpayeh·O. Tchernyshyov·C. L. Broholm·C. Pfleiderer
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Abstract

In the quest to realize a quantum spin liquid (QSL), magnetic long-range order is hardly welcome. Yet it can offer deep insights into a complex world of strong correlations and fluctuations. Much hope was placed in the cubic pyrochlore Yb$_2$Ti$_2$O$_7$ as a putative U(1) QSL but a new class of ultra-pure single crystals make it abundantly clear the stoichiometric compound is a ferromagnet. Here we present a detailed experimental and theoretical study of the corresponding field-temperature phase diagram. We find it to be richly anisotropic with a critical endpoint for $\vec{B}\,\parallel\,\langle 100\rangle$, while field parallel to $\langle 110 \rangle$ and $\langle 111 \rangle$ enhances the critical temperature by up to a factor of two and shifts the onset of the field-polarized state to finite fields. Landau theory shows that Yb$_2$Ti$_2$O$_7$ in some ways is remarkably similar to pure iron. However, it also pinpoints anomalies that cannot be accounted for at the classical mean-field level including a dramatic enhancement of $T_{\mathrm{C}}$ and reentrant phase boundary by fields with a component transverse to the easy axes, as well as the anisotropy of the upper critical field in the quantum limit.

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S. Säubert, A. Scheie, C. Duvinage, J. Kindervater, S. Zhang, H. J. Changlani, Guangyong Xu, S. M. Koohpayeh, O. Tchernyshyov, C. L. Broholm, C. Pfleiderer. 2019-12-23. Orientation Dependence of the Magnetic Phase Diagram of Yb$_2$Ti$_2$O$_7$. https://doi.org/10.1103/physrevb.101.174434

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