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arXiv · 2108.01217

The case for a U(1)$_\pi$ Quantum Spin Liquid Ground State in the Dipole-Octupole Pyrochlore Ce$_2$Zr$_2$O$_7$

E. M. Smith·O. Benton·D. R. Yahne·B. Placke·R. Schäfer·J. Gaudet·J. Dudemaine·A. Fitterman·J. Beare·A. R. Wildes·S. Bhattacharya·T. DeLazzer·C. R. C. Buhariwalla·N. P. Butch·R. Movshovich·J. D. Garrett·C. A. Marjerrison·J. P. Clancy·E. Kermarrec·G. M. Luke·A. D. Bianchi·K. A. Ross·B. D. Gaulin
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Abstract

The Ce$^{3+}$ pseudospin-$\frac{1}{2}$ degrees of freedom in the pyrochlore magnet Ce$_2$Zr$_2$O$_7$ are known to possess dipole-octupole (DO) character, making it a candidate for novel quantum spin liquid (QSL) ground states at low temperatures. We report new polarized neutron diffraction at low temperatures, as well as heat capacity ($C_p$) measurements on single crystal Ce$_2$Zr$_2$O$_7$. The former bears both similarities and differences from that measured in the canonical dipolar spin ice compound Ho$_2$Ti$_2$O$_7$, while the latter rises sharply at low temperatures, initially plateauing near 0.08 K, before falling off towards a high temperature zero beyond 3 K. Above $\sim$0.5 K, the $C_p$ data set can be fit to the results of a quantum numerical linked cluster (NLC) calculation, carried out to 4$^{\mathrm{th}}$ order, that allows estimates for the terms in the near-neighbour XYZ Hamiltonian expected for such DO pyrochlore systems. Fits of the same theory to the temperature dependence of the magnetic susceptibility and unpolarized neutron scattering complement this analysis. A comparison between the resulting best fit NLC calculation and the polarized neutron diffraction shows both agreement and discrepancies, mostly in the form of zone-boundary diffuse scattering in the non-spin flip channel, which are attributed to interactions beyond near-neighbours. The lack of an observed thermodynamic anomaly and the constraints on the near-neighbour XYZ Hamiltonian suggest that Ce$_2$Zr$_2$O$_7$ realizes a U(1)$_\pi$ QSL state at low temperatures, and one that likely resides near the boundary between dipolar and octupolar character.

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E. M. Smith, O. Benton, D. R. Yahne, B. Placke, R. Schäfer, J. Gaudet, J. Dudemaine, A. Fitterman, J. Beare, A. R. Wildes, S. Bhattacharya, T. DeLazzer, C. R. C. Buhariwalla, N. P. Butch, R. Movshovich, J. D. Garrett, C. A. Marjerrison, J. P. Clancy, E. Kermarrec, G. M. Luke, A. D. Bianchi, K. A. Ross, B. D. Gaulin. 2021-08-03. The case for a U(1)$_\pi$ Quantum Spin Liquid Ground State in the Dipole-Octupole Pyrochlore Ce$_2$Zr$_2$O$_7$. https://doi.org/10.1103/physrevx.12.021015

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