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arXiv · 2408.12656

Bond disorder in extended Heisenberg-Kitaev models: Spin textures and in-gap states in the high-field regime

Georgia Fragkopoulou·Matthias Vojta
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Abstract

We study the effect of bond disorder in extended Heisenberg-Kitaev models on the honeycomb lattice, relevant for materials such as $\alpha$-RuCl$_3$, in the semiclassical limit using a combination of T-matrix and real-space spin-wave approaches. Focusing on the regime of large applied magnetic field, we discuss two distinct but related disorder-induced phenomena, namely spin textures in the vicinity of isolated impurities and magnetic excitations below the bulk gap. A finite impurity concentration smears the field-tuned phase transition and turns the isolated in-gap states into impurity bands. As a result, there is a large field regime above the bulk transition into the high-field phase where impurity-induced states fill the bulk spin gap. We illustrate the field dependence of these in-gap states for parameters relevant for $\alpha$-RuCl$_3$, and we connect our results to heat-transport and NMR data which indicated their presence.

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Georgia Fragkopoulou, Matthias Vojta. 2024-08-22. Bond disorder in extended Heisenberg-Kitaev models: Spin textures and in-gap states in the high-field regime. https://doi.org/10.1103/physrevb.110.174444

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