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Experimental signatures of a three-dimensional quantum spin liquid in effective spin-1/2 Ce2Zr2O7 pyrochlore

Abstract

A quantum spin liquid is a state of matter where unpaired electrons’ spins, although entangled, do not show magnetic order even at the zero temperature. The realization of a quantum spin liquid is a long-sought goal in condensed-matter physics. Although neutron scattering experiments on the two-dimensional spin-1/2 kagome lattice ZnCu3(OD)6Cl2 and triangular lattice YbMgGaO4 have found evidence for the hallmark of a quantum spin liquid at very low temperature (a continuum of magnetic excitations), the presence of magnetic and non-magnetic site chemical disorder complicates the interpretation of the data. Recently, the three-dimensional Ce3+ pyrochlore lattice Ce2Sn2O7 has been suggested as a clean, effective spin-1/2 quantum spin liquid candidate, but evidence of a spin excitation continuum is still missing. Here, we use thermodynamic, muon spin relaxation and neutron scattering experiments on single crystals of Ce2Zr2O7, a compound isostructural to Ce2Sn2O7, to demonstrate the absence of magnetic ordering and the presence of a spin excitation continuum at 35 mK. With no evidence of oxygen deficiency and magnetic/non-magnetic ion disorder seen by neutron diffraction and diffuse scattering measurements, Ce2Zr2O7 may be a three-dimensional pyrochlore lattice quantum spin liquid material with minimum magnetic and non-magnetic chemical disorder.

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Fig. 1: Summary of crystal structure, CEF levels, d.c. susceptibility and specific heat of Ce2Zr2O7.
Fig. 2: Brillouin zone, diffuse neutron scattering, a.c. susceptibility and μSR data of Ce2Zr2O7.
Fig. 3: Summary of energy and wavevector dependence of the spin excitations in Ce2Zr2O7.
Fig. 4: The energy and wavevector dispersion of magnetic excitations in Ce2Zr2O7.

Data availability

The data that support the plots in this paper and other findings of this study are available from the corresponding author on reasonable request.

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Acknowledgements

We thank Y. Su, Y. J. Uemura, J. A. Rodriguez and Z. Ma for helpful discussions. The neutron scattering work at Rice is supported by US DOE BES DE-SC0012311 (P.D.). The single-crystal-growth work at Rice is supported by the Robert A. Welch. Foundation under grant no. C-1839 (P.D.). E.M. and C.-L.H. acknowledge the support from US DOE BES DE-SC0019503. A.H.N. acknowledges the support of the Robert A. Welch Foundation grant no. C-1818 and NSF CAREER grant no. DMR-1350237. Research at UCSD was supported by the US DOE BES DE-FG02-04ER46105 (M.B.M.). The work of J.-H.C. was supported by the National Research Foundation of Korea (NRF-2017K1A3A7A09016303). This research used resources at the Spallation Neutron Source and the High Flux Isotope Reactor, DOE Office of Science User Facilities operated by the ORNL. H.C. acknowledges the support of US DOE BES Early Career Award KC0402010 under contract DE-AC05-00OR22725. Crystal growth by B.G., X.X. and S.-W.C. at Rutgers was supported by the visitor programme at the Center for Quantum Materials Synthesis, funded by the Gordon and Betty Moore Foundation’s EPiQS initiative through grant GBMF6402, and by Rutgers University. G.C. acknowledges the support from the Ministry of Science and Technology of China with grant no. 2016YFA0301001 and 2016YFA0300500.

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P.D., B.G. and G.C. conceived the project. B.G., T.C., X.X. and S.-W.C. prepared the samples. d.c. magnetic susceptibility and heat capacity measurements were performed by C.-L.H. in the laboratory of E.M. a.c. susceptibility measurements were carried out by K.S., M.N., S.S. and M.B.M. μSR measurements were carried out and analysed by D.W.T. with help from C.B. and J.A.T.V. The CEF level measurements and analysis were performed by B.G., M.B.S. and D.T.A. X-ray and neutron diffraction experiments were carried out and analysed by H.C. Neutron diffuse scattering experiments were carried out by B.G. and F.Y. Inelastic neutron scattering experiments were carried out and analysed by B.G., T.C., G.S., H.H. and J.-H.C. Theoretical analysis was performed by G.C. A.H.N. helped with the initial theoretical analysis. The entire project was supervised by P.D. The manuscript was written by P.D., B.G., T.C., A.H.N. and G.C. All authors made comments.

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Correspondence to Pengcheng Dai.

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Supplementary Table 1 and Supplementary Figs. 1–7.

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Gao, B., Chen, T., Tam, D.W. et al. Experimental signatures of a three-dimensional quantum spin liquid in effective spin-1/2 Ce2Zr2O7 pyrochlore. Nat. Phys. 15, 1052–1057 (2019). https://doi.org/10.1038/s41567-019-0577-6

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