Spectroscopy of spinons in quantum spin ice: threshold enhancement and Cerenkov radiation*

Quantum spin liquids are low temperature phases of magnetic materials in which quantum fluctuations prevent the establishment of long-range magnetic order. These phases support exotic fractionalized spin excitations (spinons) and emergent gauge fields. In this talk, I will briefly review the basic theoretical picture of how a quantum Coulomb phase emerges in spin ice and then turn to recent results regarding the observable consequences in neutron scattering. The emergent Coulomb interaction modifies the threshold cross-section for spinon production dramatically, changing the weak turn-on expected from a mean-field treatment to an abrupt onset reflecting the basic coupling parameters. The slow photon typical in existing lattice models and materials suppresses the intensity at finite momentum and allows profuse Cerenkov radiation beyond a critical momentum. These features are broadly consistent with recent numerical and experimental results.