Regensburg 2025 – wissenschaftliches Programm

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TT: Fachverband Tiefe Temperaturen

TT 27: Focus Session: Nonlinear Spectroscopy of Collective Excitations in Quantum Magnets (joint session TT/MA)

TT 27.7: Vortrag

Mittwoch, 19. März 2025, 12:30–12:45, H36

Higher-Order Susceptibilities in Extended Kitaev Models Computed Via Krylov-Space Based Methods — •David Kaib, Marius Möller, and Roser Valenti — Institut für theoretische Physik, Goethe-Universität Frankfurt

Recently, it was proposed that techniques measuring higher-order dynamical response, such as two-dimensional coherent spectroscopy (2DCS), could provide more distinguishable signatures in analyzing the excitations of different systems. This is particularly true when linear response reveals only a featureless continuum, which could arise from various different types of excitations, or, for example, static disorder. The numerical evaluation of nonlinear response functions can, however, be computationally very demanding. Here, we propose an efficient Lanczos-based method that computes higher-order susceptibilities directly in the frequency domain. As an application case, we consider extended Kitaev models, that are relevant to α-RuCl₃ and related materials. We compare the nonlinear response from our method to the one obtained within linear spin-wave theory, showcasing that nonlinear response measurements can distinguish whether an observed excitation continuum is of conventional two-magnon type or has a different origin.

Keywords: Kitaev materials; Nonlinear response; Two-dimensional coherent spectroscopy; Frustrated magnetism; Exact Diagonalization