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RCQM/FCMP: N. Peter Armitage: Bond dependent interactions in Co based magnets: chains and honeycomb

Talk Date: Tuesday, 10/17/2023, 2:30 PM (CDT) Speaker: N. Peter Armitage Institution: John Hopkins University Title: Bond dependent interactions in Co based magnets: chains and honeycomb Abstract: Kitaev quantum spin liquids (QSLs) are exotic states of matter that are predicted to host Majorana fermions and gauge flux excitations. However, so far all known Kitaev QSL candidates are known to have appreciable non-Kitaev interactions that pushes these systems far from the QSL regime. Co based magnets have been proposed to be perhaps a more ideal platform for realizing Kitaev QSLs. In this talk I will show evidence for a Kitaev interactions in the quasi-one-dimensional ferromagnet CoNb2O6. Although it is usually believed to be the best material realization of a 1D Ising chain, by combining terahertz spectroscopy and calculations we have shown that CoNb2O6 is well described by a model with bond-dependent interactions. We call this model the ‘twisted Kitaev chain’, as these interactions are similar to those of the honeycomb Kitaev spin liquid. The ferromagnetic ground state of CoNb2O6 arises from the compromise between two axes. Owing to this frustration, even at zero field domain walls have quantum motion, which is described by the celebrated Su–Schriefer–Heeger model of polyacetylene and shows rich behavior as a function of field. Most recently, we have also investigated the honeycomb cobalt-based magnet, BaCo2(AsO4)2, which was also proposed to have Kitaev interactions. The physics of this system and evidence for bond directional exchanges will be discussed. References: [1] Z. Zhang et al. Nature Materials 22, 58-63 (2023). [2] Y. Xu et al., Phys. Rev. X 12, 021020 (2022).