Quantum Dynamics of Magnetic Skyrmions: Consistent Path Integral Formulation

TL;DR

This paper develops a quantum path integral formalism to describe skyrmion dynamics at finite temperatures, revealing temperature-dependent, non-local damping effects originating from magnon interactions, with implications for spin caloritronics.

Contribution

It introduces a novel path integral approach to quantum skyrmion dynamics, explicitly deriving temperature-dependent damping and inertia from magnon coupling, advancing understanding of topological magnetic textures.

Findings

Intrinsic damping is highly non-local and quantum-mechanical in nature.

Damping increases with temperature and magnetic field, affecting skyrmion motion.

Modified Thiele's equation includes non-local dissipative and mass terms at high temperatures.

Abstract

We present a path integral formalism for the intrinsic quantum dynamics of magnetic skyrmions coupled to a thermal background of magnetic fluctuations. Upon promoting the skyrmion's collective coordinate $\boldsymbol{R}$ to a dynamic variable and integrating out the magnonic heat bath, we derive the generalized equation of motion for $\boldsymbol{R}$ with a non-local damping term that describes a steady-state skyrmion dynamics at finite temperatures. Being essentially temperature dependent, the intrinsic damping is shown to originate from the coupling of thermally activated magnon modes to the adiabatic potential driven by a rigid skyrmion motion, which can be regarded as another manifestation of emergent electrodynamics inherent to topological magnetic textures. We further argue that the diagonal components of the damping term act as the source of dissipation and inertia, while its off-diagonal components modify the gyrotropic motion of a magnetic skyrmion. By means of numerical calculations for the lattice spin model of chiral ferromagnets, we study the temperature behavior of the intrinsic damping as a function of magnetic field in periodic and confined geometries. The intrinsic damping is demonstrated to be highly non-local, revealing its quantum-mechanical nature, that becomes more pronounced with increasing temperature. At high temperatures when the magnon occupation factors are large, the intrinsic damping is shown to yield a modified Thiele's equation with the additional non-local dissipative and mass terms that exhibit an almost linear temperature behavior. Our results provide a microscopic background for semiclassical magnetization dynamics and establish a framework for understanding spin caloritronics effects in topological magnetic textures.