Nonlinear spectroscopy in extended Kitaev models: Contrasting spin liquids and ordered phases*

Nonlinear spectroscopy is being considered as a potentially powerful tool to distinguish coherent fractionalized excitations from effects of disorder or finite lifetime in linear response excitation continua [1]. In this spirit, various recent theoretical studies [2-4] have analyzed nonlinear response in the exactly solvable Kitaev honeycomb model, known for its spin liquid state and fractionalized excitations. In our study, we move to extended Kitaev models that are relevant for the description of real Kitaev candidate materials. As these models are not exactly solvable, we develop methods to efficiently calculate nonlinear response functions numerically on finite-size systems. Analyzing the response of various extended models, many with magnetically ordered states, we point out differences and similarities to the nonlinear response of the pure Kitaev model. This should be relevant for the interpretation of future experiments. 

[1] Wan and Armitage, PRL 122, 257401 (2019)

[2] Choi et al., PRL 124, 117205 (2020)

[3] Kanega et al., PRR 3, L032024 (2021)

[4] Krupnitska and Brenig, arXiv:2304.06076