Nonequilibrium Skyrmion Dynamics under Oscillating Magnetic Fields

We extend earlier studies on the quantum propagation of a skyrmion in chiral magnetic insulators [1], to include the effects of time periodic magnetic field gradients on skyrmion dynamics [2]. The unavoidable coupling of the external field to the magnons gives rise to time-dependent dissipation for the skyrmion, with measurable consequences on the skyrmion path. These ac fields act as a net driving force on the skyrmion via its own intrinsic magnetic excitations. We generalize the standard quantum theory of dissipation to include the stochastic effects of the driven bath on the skyrmion dynamics. We address the stochastic effects of the quantum driven bath on the skyrmion propagation [3], and provide a generalized version of the nonequilibrium fluctuation-dissipation relation for externally driven reservoirs. We also predict a novel fast thermal activation for the mean-square displacement that scales quadratically with temperature in the experimentally accessible low-temperature regime.

[1] C. Psaroudaki, S. Hoffman, J. Klinovaja, and D. Loss, Quantum Dynamics of Skyrmions in Chiral Magnets, Phys. Rev. X 7, 041045 (2017).
[2] C. Psaroudaki and D. Loss, Skyrmions Driven by Intrinsic Magnons, Phys. Rev. Lett. 120, 237203 (2018).
[3] C. Psaroudaki, P. Aseev, and D. Loss, Phys. Rev. B 100, 134404 (2019).