High-energy spin excitations in the quantum spin liquid candidate Zn-substituted barlowite probed by resonant inelastic x-ray scattering

A quantum spin liquid is a novel ground state that can support long-range entanglement between magnetic moments, resulting in exotic spin excitations involving fractionalized S=12 spinons. Here, we measure the excitations in single crystals of the spin liquid candidate Zn-barlowite using resonant inelastic x-ray scattering. By analyzing the incident polarization and temperature dependences, we deduce a clear magnetic scattering contribution forming a broad continuum that surprisingly extends up to ∼200 meV (∼14J, where J is the magnetic exchange). The excitation spectrum indicates that significant contributions may arise from multiple pairs of spinons and/or antispinons at high energies. Furthermore, the observation of similar scattering in the hexagonal barlowite parent material above its ordering temperature suggests the presence of similar high-energy excitations, irrespective of the low-energy physics.