Are the Ce pyrochlores quantum spin liquids - and how could we know for sure?

Three-dimensional U(1) quantum spin liquids (QSLs) have long been sought as condensed-matter realizations of emergent quantum electrodynamics (QED). This emergent QED is rendered all the more intriguing by the presence of magnetic monopoles, strongly coupled to slow “photons”. Quantum spin ices - arising in pyrochlore magnets with dominant Ising interactions supplemented by transverse exchange - are among the most promising platforms for this physics. Yet, in practice, many candidate materials have fallen short as structural disorder, off-stoichiometry, or competing ordered states have obscured or destroyed the U(1) QSL phase.

Over the last decade, the family of Ce pyrochlores Ce₂M₂O₇ (M = Zr, Sn, Hf) has emerged as perhaps the most likely experimental setting for realizing a U(1) QSL. The Kramers nature of the Ce³⁺ ion provides some protection against disorder, while its dipolar–octupolar ground-state doublet gives rise to an anisotropic XYZ Hamiltonian that theoretically stabilizes the U(1) QSL over a wide parameter range.

In this talk I will review recent progress in understanding these materials, with a view to evaluating the status of each one as a candidate U(1) QSL. While there are many commonalities between the Ce pyrochlores there are also subtle differences, which may suggest different interpretations for each material.

Finally, I will discuss how nonlinear spectroscopy could provide a powerful tool for directly identifying spinon dynamics in quantum spin ice systems, and outline how such measurements might be applied to the Ce pyrochlores.