pyrochlore*

A quantum spin liquid (QSL) is an exotic state of matter where unpaired electrons’ spins, although being entangled, do not show magnetic order even at the zero-temperature. Because such a state may be important to the microscopic origin of high-transition temperature superconductivity and useful for quantum computation, the experimental realization of QSL is a long-sought goal in condensed matter physics. Previous neutron scattering experiments on the two-dimensional QSL candidates ZnCu₃(OD)₆Cl₂ and YbMgGaO₄ have found evidence for the hallmark of a QSL at very low temperature - a continuum of magnetic excitations. However, the presence of site disorder complicates the interpretation of the data. Recently, the three-dimensional (3D) Ce³⁺ pyrochlore lattice Ce₂Sn₂O₇ has been suggested as a clean, effective spin-1/2 QSL candidate, but the evidence of a spin excitation continuum is missing due to the lack of single crystals. Until 2019, the first single-crystal study of Ce₂Zr₂O₇, a compound isostructural to Ce₂Sn₂O7, reveals the absence of magnetic ordering/spin-glass down to 20 mK and the presence of a spin excitation continuum at 35 mK. With no evidence of oxygen deficiency and chemical disorder seen by diffuse scattering measurements and neutron diffraction, Ce₂Zr₂O₇ may be a 3D pyrochlore lattice QSL material with minimum magnetic and nonmagnetic chemical disorder. Recent works including elastic and inelastic neutron scattering measurements under magnetic fields, as well as diffusive scattering in Ce₂Zr₂O₇ in large Q ranges, may help identify the system as an octupolar U(1) QSL.