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. Although 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, 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. Here we use alternating current magnetic susceptibility, thermodynamic, muon spin relaxation (μSR), and neutron scattering experiments on single crystals of Ce₂Zr₂O₇, a compound isostructural to Ce₂Sn₂O₇, to demonstrate 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.