Unveiling dynamical signatures of dipolar-octupolar quantum spin ice*

Recent experiments on Ce₂Zr₂O₇ suggest that this material may host a novel form of quantum spin ice, a three-dimensional quantum spin liquid with an emergent photon. The Ce³⁺ local moments on the pyrochlore lattice are described by pseudospin 1/2 degrees of freedom, whose components transform as dipolar and octupolar moments under symmetry operations. In principle, there exist four possible quantum spin ice regimes, depending on whether the Ising component is in the dipolar/octupolar channel, and two possible flux configurations of the emergent gauge field. We theoretically investigate dynamical spin structure factors in all four quantum spin ice regimes using computations on quantum and classical models, which include exact diagonalization, molecular dynamics, and gauge mean-field theory. Contrasting the distinct signatures of quantum and classical results for the four possible quantum spin ice regimes and elucidating the role of quantum fluctuations, we show that the quantum dynamical structure factor computed for the π-flux octupolar quantum spin ice regime is most compatible with the neutron scattering results on Ce₂Zr₂O₇. We also suggest an ultrasound experiment that can detect the emergent photon excitations in this system.