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

Abstract

Ce-pyrochlores, Ce$_2$X$_2$O$_7$ (X = Sn, Hf, Zr), have gained much recent attention as new quantum spin ice (QSI) ground state candidates. Although the nearest-neighbor (NN) XYZ model has been the prevailing theoretical framework, its adequacy has been questioned by bulk measurements on Ce$_2$Hf$_2$O$_7$ and Ce$_2$Zr$_2$O$_7$, suggesting the relevance of further-neighbor interactions at low temperatures. However, clearly disentangling their effects from structural disorder has been challenging with samples grown by conventional methods. Here, we overcome this limitation and report diffuse neutron scattering measurements on Ce$_2$Sn$_2$O$_7$ single crystals synthesized by hydrothermal methods, with substantially reduced structural disorder compared to our previous floating-zone-grown samples. Our results unambiguously demonstrate the inadequacy of the NN model by falsifying its central prediction for Ce$_2$Sn$_2$O$_7$ -- a transition to an all-in-all-out (AIAO) magnetic order. Importantly, we observe neither long-range nor short-range AIAO order near the predicted $\mathrm{T_N}$, indicating that further neighbor interactions must play a non-perturbative role in determining the low-temperature spin correlations in Ce$_2$Sn$_2$O$_7$. Notably, we find that the diffuse scattering in Ce$_2$Sn$_2$O$_7$ is nearly identical to that of the classical dipolar spin ice Dy$_2$Ti$_2$O$_7$, which provides key insights into the organizing principles of the low-energy manifold in the presence of such interactions.