Langevin dynamics of generalized spins as SU(<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mi>N</mml:mi></mml:math>) coherent states

Abstract

Quantum spin states often contain additional structure beyond the usual angular momentum dipole. The classical Landau-Lifshitz spin dynamics may be generalized to model the coupled dynamics of dipoles, quadrupoles, and higher order multipoles. This paper introduces temperature-dependent Langevin noise and damping terms to the generalized spin dynamics. High numerical efficiency is possible by working with coherent states in the Schr\"odinger picture. The method is illustrated via simulation of magnetic skyrmion dynamics both in and out of equilibrium.