Faculty Publication News: Kemp Plumb in Nature Communications

Physics Department Chair Vesna Mitrivić congratulated Assistant Professor Kemp Plumb on his recently published paper "Momentum-independent magnetic excitation continuum in the honeycomb iridate H3LiIr2O6" in Nature Communications, saying, "This is a very important publication." 

In summarizing the manuscript, Prof. Plumb explains that "Quantum spin liquids are novel states of matter where a magnetic material's constituent magnetic moments do not freeze, even near absolute zero, and are defined by the presence of long-range entanglement. The Kitaev spin liquid is one  type of spin liquid that has been theoretically predicted, but not observed. There are a number of candidate materials for this state, but H3LiIr2O6 is the only candidate Kitaev compound absent of long-range magnetic order and frozen moments and it may be a unique example of the long-sought quantum spin liquid. However, disorder is fundamental to the physics of this material. Even in crystallographically pristine samples, hydrogen zero-point motion randomly modulates the strength of the magnetic interactions. What remains to be understood is how such disorder can act to generate a ground state absent of any frozen moments but with low-energy spin excitations.  Since disorder is prevalent among quantum materials,  H3LiIr2O6 stands as an emblem of a major and central challenge facing the field of quantum spin liquids: how are we to understand the ground states that arise from an interplay of disorder and quantum correlations?

The measurements presented in this work address this challenge by revealing the full spectrum of collective excitations that characterize magnetic correlations in H3LiIr2O6. The result is striking for the complete lack of momentum dependence of an intense high-energy continuum of excitations signifying the predominance of quantum fluctuations on top of a disordered background. In light of our measurements, H3LiIr2O6 must be considered a new phase of disordered matter, distinct from a spin glass or paramagnet. The data support the interpretation of H3LiIr2O6 as a disordered topological phase in close proximity to the Kitaev quantum spin liquid.    

By elucidating the dynamic response of an important bond-disordered frustrated magnet, our results deepen the understanding of the interplay between disorder, competing interactions, and quantum fluctuations in quantum materials."

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