Inelastic neutron scattering studies of the role of interlayer spins in the kagome quantum magnets barlowite and Zn-barlowite*

Geometrically frustrated spins on kagome lattices may exhibit long-range entanglement in the form of a quantum spin liquid (QSL) ground state. Substituting inter-kagome-layer copper atoms in barlowite (Cu₄(OH)₆Cl₂) with zinc atoms yields Zn-barlowite (Zn_xCu_4-x(OH)₆Cl₂), which has emerged as a recent candidate QSL material. In real growths, this substitution is imperfect (x<1), and some magnetic atoms remain between kagome layers. Ground states of impurity-affected kagome lattices are still poorly understood and open questions remain on how impurities may modify QSL states in frustrated magnets. This talk highlights recent inelastic neutron scattering measurements on barlowite and on large single crystals of Zn-barlowite. Quantitative analyses and comparisons of these data uncover kagome-to-interlayer coupling behaviors and elucidate how interlayer spins may affect magnetic ordering in barlowite and QSL formation in Zn-barlowite.