Case for a U(1)_{π} Quantum Spin Liquid Ground State in the Dipole-Octupole Pyrochlore Ce_{2}Zr_{2}O_{7}

Abstract

The Ce^{3+} pseudospin-1/2 degrees of freedom in the pyrochlore magnet Ce_{2}Zr_{2}O_{7} 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 (C_{p}) measurements on single crystal Ce_{2}Zr_{2}O_{7}. The former bears both similarities and differences with that measured from the canonical dipolar spin ice compound Ho_{2}Ti_{2}O_{7}, 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 C_{p} 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 Ce_{2}Zr_{2}O_{7} 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.