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Title: Has emergent quantum electrodynamics been observed in a quantum spin ice?
Plain: Quantum spin ice should host three kinds of emergent particles: photons, electric-like spinons and magnetic monopoles. Cerium pyrochlores such as Ce2Zr2O7 show signs of these, but alternative explanations are not fully excluded.
Precise: In Ce2Zr2O7, Ce2Sn2O7 and Ce2Hf2O7 (dipolar-octupolar doublets), establish the $\mathrm{U}(1)$ quantum spin liquid through its distinct signatures: a gapless linearly dispersing transverse photon ($C \sim T^{3}$ well below the photon bandwidth), a spinon continuum, and their predicted spectral weights. An answer is a fit of thermodynamic and neutron data by quantum spin ice theory with independently fixed exchange parameters that excludes classical or disorder-driven alternatives.
Settled by: Polarized neutron scattering below $0.05\,\mathrm{K}$ resolving the low-energy photon mode and heat capacity showing the $T^3$ term, both matched to quantum Monte Carlo of the fitted XYZ model.
Kind: phenomenon
Answer type: identification
References: (empty)
Literature status: partially-resolved
Status note: Gao et al. (Nature Physics 2025) reported neutron and thermodynamic evidence for emergent photons and spinons in Ce2Zr2O7, interpreted as a pi-flux quantum spin ice.
Posed since: 2004