Observation of Dipolar Spin-ice--like Correlations in the Quantum Spin Ice Candidate Ce$_2$Sn$_2$O$_7$

The Ce$_2$X$_2$O$_7$ (X=Sn, Hf, Zr) family of cubic pyrochlores has emerged as one of the most promising classes of Quantum Spin Ice candidates. However, understanding their microscopic exchange Hamiltonian and spin correlations has been hampered by varying sample quality, and poor signal-to-noise in the existing neutron data due to a small Ce$^{3+}$ magnetic dipole moment. In this work, we overcome these challenges and report single-crystal diffuse neutron scattering from hydrothermally grown Ce$_2$Sn$_2$O$_7$ -- the highest quality crystals obtained to date for the Ce$_2$X$_2$O$_7$ family. In contrast to the broad diffuse scattering observed in Ce$_2$Hf$_2$O$_7$ and Ce$_2$Zr$_2$O$_7$, we find highly structured diffuse scattering from Ce$_2$Sn$_2$O$_7$ featuring strong intensities along the Brillouin zone boundaries. The observed $\mathbf{Q}$-dependence disagrees with predictions of the nearest neighbour XYZ model commonly used for Ce$_2$X$_2$O$_7$, but is remarkably similar to the diffuse scattering observed in \textit{classical} Dipolar Spin Ice. Our study highlights the importance of further neighbour interactions in determining the low energy physics of the Ce-pyrochlores, and calls for a revision of the current theoretical framework to incorporate their effects.