FBr—a kagome quantum antiferromagnet*

Barlowite is the parent compound of a new kagome quantum spin liquid candidate Zn-barlowite. We synthesized a new variant of barlowite with a higher symmetry crystal structure at low temperatures. This new high-symmetry barlowite undergoes two consecutive magnetic transitions below ~10 K. Our previous elastic neutron scattering revealed that in the ground state the spins order in a pinwheel q=0 structure, while between the two magnetic transition temperatures the kagome spins likely form a novel valence bond crystal (VBC). In this talk, I will present our recent inelastic neutron scattering data taken on coaligned crystals. The data collected in both the spin ordered and the VBC states exhibit distinct features that cannot be explained by trivial spin waves. Our study provides crucial information regarding the exotic spin excitations in barlowite.