Case for a U(1)π Quantum Spin Liquid Ground State in the Dipole-Octupole Pyrochlore Ce2Zr2O7

The Ce3+ pseudospin-1/2 degrees of freedom in the pyrochlore magnet Ce2Zr2O7 are known to possess dipole-octupole character, making it a candidate for novel quantum spin liquid ground states at low temperatures. We report new polarized neutron diffraction at low temperatures, as well as heat capacity (Cp) measurements on single crystal Ce2Zr2O7. The former bears both similarities and differences with that measured from the canonical dipolar spin ice compound Ho2Ti2O7, while the latter rises sharply at low temperatures, initially plateauing near 0.08 K, before falling off toward a high temperature zero beyond 3 K. Above∼0.5 K, the Cp dataset can be fit to the results of a quantum numerical linked cluster calculation, carried out to fourth order, that allows estimates for the terms in the near-neighbor XYZ Hamiltonian expected for such dipole-octupole pyrochlore systems. Fits of the same theory to the temperature dependence of the magnetic susceptibility and unpolarized neutron scattering complement this analysis. A comparison between the resulting best-fit numerical linked cluster calculation and the polarized neutron diffraction shows both agreement and discrepancies, mostly in the form of zone-boundary diffuse scattering in the non-spin-flip channel, which are attributed to interactions beyond near neighbors. The lack of an observed thermodynamic anomaly and the constraints on the near-neighbor XYZ Hamiltonian suggest that Ce2Zr2O7 realizes a U(1)π quantum spin liquid state at low temperatures, and one that likely resides near the boundary between dipolar and octupolar character.