Leveraging thermal fluctuations to study the spin dynamics of quantum magnets

Low-dimensional or frustrated quantum (S = 1/2) magnets exhibit strong quantum spin fluctuations, leading to complex spin dynamics that challenge conventional spin-wave analysis and complicate the identification of microscopic spin models. However, raising the temperature moves these systems into a regime dominated by classical thermal fluctuations, rendering their dynamical properties more amenable to semi-classical analysis. In this presentation, we introduce a new approach that leverages thermal fluctuations to study the momentum and energy-resolved spin dynamics of quantum magnets, using the Landau-Lifshitz dynamics (LLD) framework implemented in the Su(n)ny software package [1]. We explain our standardized simulation protocol designed for modelling finite-temperature spin dynamics in S = 1/2 systems and present its successful application to the S = 1/2 square lattice Heisenberg antiferromagnet Zn₂VO(PO₄)₂ [1] and the S = 1/2 XXZ triangular lattice antiferromagnet Ba₂La₂CoTe₂O₁₂ [2]. Notably, this approach has successfully identified the spin Hamiltonians by fitting energy-resolved excitation spectra in the paramagnetic phase, while also capturing the attenuation of quantum spin dynamics (e.g., continuum excitations) due to thermal fluctuations. We conclude by discussing the broad potential of the LLD-based approach in advancing the understanding of cutting-edge topics in quantum magnetism.