paper

Single Crystal Diffuse Neutron Scattering Study of the Dipole-Octupole Quantum Spin Ice Candidate Ce $_{2}$ Zr $_{2}$ O $_{7}$ : No Apparent Octupolar Correlations Above $T = 0.05$ K

arXiv:2407.07640 · doi:10.1103/PhysRevX.15.021033

Abstract

The insulating magnetic pyrochlore Ce $_{2}$ Zr $_{2}$ O $_{7}$ has gained attention as a quantum spin ice candidate with dipole-octupole character arising from the crystal electric field ground state doublet for the Ce $^{3 +}$ ion. This permits both spin ice phases based on magnetic dipoles and those based on more-exotic octupoles. We report low-temperature neutron diffraction measurements on single crystal Ce $_{2}$ Zr $_{2}$ O $_{7}$ with $Q$ -coverage both at low $Q$ where the magnetic form factor for dipoles is near maximal and at high $Q$ where the magnetic form factor for Ce $^{3 +}$ octupoles is near maximal. This study was motivated by recent powder neutron diffraction studies of other Ce-based dipole-octupole pyrochlores, Ce $_{2}$ Sn $_{2}$ O $_{7}$ and Ce $_{2}$ Hf $_{2}$ O $_{7}$ , which each showed temperature-dependent diffuse diffraction at high $Q$ that was interpreted as arising from octupolar correlations. Our measurements use an optimized single crystal diffuse scattering instrument that allows us to screen against strong Bragg scattering from Ce $_{2}$ Zr $_{2}$ O $_{7}$ . The temperature-difference neutron diffraction reveals a low- $Q$ peak consistent with dipolar spin ice correlations reported in previous work, and an alternation between positive and negative net intensity at higher $Q$ . These features are consistent with our numerical-linked-cluster calculations using pseudospin interaction parameters previously reported for Ce $_{2}$ Zr $_{2}$ O $_{7}$ , Ce $_{2}$ Sn $_{2}$ O $_{7}$ , and Ce $_{2}$ Hf $_{2}$ O $_{7}$ . Importantly, neither the measured data nor any of the NLC calculations show evidence for increased scattering at high $Q$ resulting from octupolar correlations. We conclude that at the lowest attainable temperature for our measurements ( $T = 0.05$ K), scattering from octupolar correlations in Ce $_{2}$ Zr $_{2}$ O $_{7}$ is not present in the neutron diffraction signal on the level of our observation threshold of ~ 0.1 % of the low- $Q$ dipole scattering.

Single Crystal Diffuse Neutron Scattering Study of the Dipole-Octupole Quantum Spin Ice Candidate Ce2​Zr2​O7​: No Apparent Octupolar Correlations Above T=0.05 K

Abstract

Single Crystal Diffuse Neutron Scattering Study of the Dipole-Octupole Quantum Spin Ice Candidate Ce $_{2}$ Zr $_{2}$ O $_{7}$ : No Apparent Octupolar Correlations Above $T = 0.05$ K