Meta-Analysis of Effective Spin Models for α-RuCl₃ from Paramagnetic Continuum Excitations

A continuum-like signal in neutron scattering is a hallmark of quasiparticle fractionalization, and notably, such a signal can persist even at high temperatures. α-RuCl3, the most promising candidate for realizing a Kitaev spin liquid, is one of the few materials exhibiting a high-temperature continuum response. This continuum has traditionally been interpreted as a manifestation of confined itinerant Majorana excitations. However, extensive studies have revealed that the effective Hamiltonian of α-RuCl3 contains substantial non-Kitaev interactions, placing it far from the pure Kitaev limit. Here, using quantum-equivalent classical spin dynamics, we fully reproduce the high-temperature continuum excitations of α-RuCl3 near the Brillouin zone center. Furthermore, by systematically testing 38 previously reported parameter sets of {J1, K, Γ, Γ', J3}, we identify the optimal model that accounts for the temperature-dependent dynamical spin structure factor. Our semi-classical approach offers a new framework for determining effective models of quantum magnets that exhibit broad continua.