Evidence for Rare Quantum Disordered Symmetry-enriched U (1) 3D Quantum Spin Liquid (QSL) Phase in Dipolar-Octupolar pseudospin, effective spin-(1/2) Pyrochlores Magnet Ce₂Zr₂O₇.

Embodied spin, orbital and lattice degrees of freedom guide the advances in quantum magnetism. Since Anderson’s proposal investigation for QSLs topological magnets with fractionalized excitations become important. Quantum Spin-Ice (QSI) are promising proprietors for QSL. In QSL collective spins excitations are described by U (1) lattice gauge theory. Ice-rules in hexagonal water ice model of frustrated material by Pauling, lead to ground state residual finite entropy. Ice rules type frustration redeemed in framework of charge order on pyrochlore, magnetic analogues of water ice. Ce₂Zr ₂O₇ is an insulator with 4f¹ Ce³⁺ degrees of freedom decorating pyrochlore lattice, network of corner-sharing tetrahedra, archetype for 3D-geometrical frustration. Experimental evidence on Ce₂Zr₂O₇ above T=0.05 K shows no evidence of ordered state, suggests it may host novel QSI, 3D QSL with emergent photon. High energy neutron spectroscopy reveals crystal field ground state doublet originating from J=5/2, comprised m_J=±3/2, resulting pseudospin S_effective=1/2 degree of freedom, components transform as dipolar and octupolar moments under symmetry operations, arises from strong spin orbit coupling and crystal field effects. Theoretical modelling of heat capacity, magnetic susceptibility and neutron scattering data estimates terms in near-neighbor microscopic effective XYZ Hamiltonian, supports presence of U (1) novel QSL, ordered All-In All-Out ground state near boundary of dipolar and octupolar nature.