Seminar — Inertial spin dynamics driven by baths characterised by a multi-Lorentzian spectral density

Recently, a quantum-thermodynamically consistent theory suitable for describing the dynamics of spins in magnetic materials, including non-Markovian effects and coloured noise was proposed by Anders et al. According to this theory, the spins are coupled to bosonic baths that are characterised by Lorentzian spectral densities [1]. The dynamics can be simulated using the Julia library 'SpiDy'[2]. Despite the success of the model, the question arises whether a single Lorentzian peak is always sufficient to describe the spectral density of real materials. The spectral density is directly linked to the density of states and many materials exhibit a structured density of state with multiple peaks. Therefore, a multi-Lorentzian spectral density may provide a better way of capturing more spectral details, leading to more accurate dynamics.

In this talk, I will give an overview of how this model can be expanded to the two cases of a single spin couplingeither to multiple independent Lorentzian baths or to a single bath characterised by a multi-Lorentzian spectraldensity. Both cases are very similar and can lead to noticeable differences in the dynamics compared to the singleLorentzian case. Emphasis is placed on the spectral analysis of the resulting spin trajectories in the differentcoupling cases.

[1] J. Anders, C. R. J. Sait, and S. A. R. Horsley, “Quantum Brownian motion for magnets”, NewJournal of Physics 24, 033020 (2022).

[2] S. Scali et al., “SpiDy.jl: open-source Julia package for the study of non-Markovian stochastic dynamics”, Journal of Open Source Software 9, 6263 (2024)