Magnetic excitations in hyperkagome iridate Na4Ir3O8

The hyperkagome iridate Na4Ir3O8 has been attracting attentions as a candidate for three-dimensional quantum spin liquid. The S = 1/2 Heisenberg antiferromagnetic model on a frustrated hyperkagome lattice has been originally studied to understand the spin-liquid behavior. In fact, strong spin-orbit coupling of Ir likely yields other anisotropic magnetic interactions which superpose on the Heisenberg coupling. The magnetic interactions in Na4Ir3O8 thus can be more complex than the pure Heisenberg model, and further experimental investigations should be required. However, the strong neutron absorption of natural Ir has hampered the investigation of magnetic excitations by neutron scattering. We try to obtain the information of magnetic interactions by inelastic neutron scattering on MERLIN with using 193Ir enriched sample which substantially reduces neutron absorption.