Probing Intrinsic and Magnetic Impurity Excitations in Single Crystals of the Kagome Quantum Spin Liquid Candidate Zn-Barlowite Using Inelastic Neutron Scattering*

The spin-1/2 Heisenberg antiferromagnet on 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 relatively new 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, with an A-B-C kagome layer stacking). This makes Zn-Barlowite promising as a potentially more pristine KAF QSL host and allows us to investigate the universality of the underlying kagome spin physics. Previous in-plane inelastic neutron scattering preformed by our group demonstrate a universality of behavior for excitations between Herbertsmithite and Zn-Barlowite at energies above ~1 meV, suggesting that these excitations arise from the similar undistorted spin-1/2  kagome layers that these materials host. Meanwhile, the excitations below 1 meV are qualitatively very different between the materials and therefore likely arise from interlayer magnetic impurities given the different impurity environments in these materials. In this talk, I present new out of plane inelastic neutron scattering data taken in Zn-Barlowite. This helps to shed light on the magnetic impurity excitations in this material so that more firm conclusions can be made about the intrinsic kagome layer physics.