MS19-04 - Crystal Structure and Isotope Effect in Quantum Liquid H3LiIr2O6

Alexandra Gibbs (ISIS Neutron and Muon Source, United Kingdom)

The search for realisations of the Kitaev model on a honeycomb lattice has recently led to the discovery of  H3LiIr2O6, lacking long-range order down to 50 mK and displaying experimental signatures consistent with a spin liquid ground state. Although the Ir-O network and its distortions are fundamental to the bond-dependent interactions on the honeycomb lattice, theoretical work suggests the inter-layer hydrogen and its ordering is crucial to understanding the intriguing behavior of H3LiIr2O6. Upon deuterium substitution, the antiferromagnetic couplings are enhanced but the liquid state remains robust. Structural studies to date have relied on X-ray diffraction which is unable to locate hydrogen / deuterium ions in the presence of heavy iridium, requiring the intuiting of possible positions based on crystal chemistry and knowledge of similar layered materials.Recently we have used the isotope effect on H3LiIr2O6 to study the effect of the inter-layer species. In addition we have taken advantage of recent developments in the use of 193Ir enrichment. The structures of H37Li193Ir2O6 and D37Li193Ir2O6 have been elucidated using high resolution neutron diffraction, allowing the crucial determination of the hydrogen/deuterium positions and studies of disorder. The results of these detailed structural studies and their link to the isotope effect on physical properties will be discussed within the context of recent theoretical work and future materials design.