Momentum-independent magnetic excitation continuum in the honeycomb iridate H3LiIr2O6

Kitaev quantum spin liquids are an exciting potential platform for hosting rich condensed matter physics. Here, the authors characterize the most promising material candidate, the honeycomb iridate H3LiIr2O6 and reveal a broad continuum of collective excitations absent of a momentum dependence-suggestive of a disordered topological spin liquid. Understanding the interplay between the inherent disorder and the correlated fluctuating-spin ground state is a key element in the search for quantum spin liquids. H3LiIr2O6 is considered to be a spin liquid that is proximate to the Kitaev-limit quantum spin liquid. Its ground state shows no magnetic order or spin freezing as expected for the spin liquid state. However, hydrogen zero-point motion and stacking faults are known to be present. The resulting bond disorder has been invoked to explain the existence of unexpected low-energy spin excitations, although data interpretation remains challenging. Here, we use resonant X-ray spectroscopies to map the collective excitations in H3LiIr2O6 and characterize its magnetic state. In the low-temperature correlated state, we reveal a broad bandwidth of magnetic excitations. The central energy and the high-energy tail of the continuum are consistent with expectations for dominant ferromagnetic Kitaev interactions between dynamically fluctuating spins. Furthermore, the absence of a momentum dependence to these excitations are consistent with disorder-induced broken translational invariance. Our low-energy data and the energy and width of the crystal field excitations support an interpretation of H3LiIr2O6 as a disordered topological spin liquid in close proximity to bond-disordered versions of the Kitaev quantum spin liquid.

Automated summary

The authors characterize the material candidate H3LiIr2O6 and find a broad continuum of collective excitations absent of a momentum dependence, suggesting a disordered topological spin liquid. Understanding the interaction between inherent disorder and the fluctuating-spin ground state is crucial for the search of quantum spin liquids.