Probing Spinon Excitations in Single Crystals of the Kagome Quantum Spin Liquid Candidate Zn-barlowite Using Inelastic Neutron Scattering.*

The spin-½ Heisenberg antiferromagnet on the kagome lattice (KAF) is among the most promising models which could host a quantum spin liquid (QSL) in two-dimensions. Zn-Barlowite (Zn_xCu_4-x(OH)₆BrF) is a newly discovered KAF material that shows strong signatures of a QSL ground state, including no measured magnetic order down to 50mK. Excitingly, Zn-Barlowite has a different interlayer impurity environment and a simpler A-A kagome layer stacking as compared to the related KAF material Herbersmithite (Zn_xCu_4-x(OH)₆Cl₂). This makes it promising as a potentially more pristine KAF QSL host and allows us to investigate the universality of the underlying kagome spin physics. Recently we have successfully synthesized millimeter-size single domain crystals of deuterated Zn-Barlowite. This allowed us to perform inelastic neutron scattering measurements on a large co-aligned crystal assembly for the first time. At high energies above ~1meV the magnetic scattering in Zn-barlowite is qualitatively similar to Herbersmithite’s and is likely due to kagome layer spinon excitations. However, there are clear differences in the low energy magnetic excitations. In Herbersmithite, it is dominated by nearest neighbor impurity correlations, whereas in Zn-Barlowite this magnetic impurity contribution is considerably smaller and cannot account for all observed magnetic excitations. Our data sheds new light on the KAF magnetic excitations and helps to gain a more unambiguous understanding of kagome QSL physics.