Robust scenario for the generation of non-equilibrium topological fluctuation states

TL;DR

This paper investigates the physics of topological fluctuation states in magnetic systems, revealing their origin from skyrmion nucleation and decay dynamics, and proposes a robust scenario for their generation using ultrafast laser excitation.

Contribution

It introduces a new understanding of topological fluctuation states, showing they arise from skyrmion dynamics and can be generated in various magnetic systems.

Findings

Topological fluctuation states appear after laser excitation without stable skyrmions.

Fluctuations originate from competition between skyrmion nucleation and decay.

Stable skyrmions freeze out when system cools faster than decay time.

Abstract

The recently discovered topological fluctuation state provides a fascinating new perspective on the ultrafast emergence of topology in condensed matter systems. However, rather little is known about the physics of this state and the origin of the topological fluctuations. Using time-resolved small-angle x-ray scattering, we observe that topological fluctuation states appear after laser excitation even if the final state does not host stable skyrmions. Simulations support these findings and reveal that the fluctuations originate from the competition between spontaneous nucleation and decay of skyrmions, consistent with Arrhenius-like activation over a potential barrier. Stable skyrmions can freeze out of such fluctuations when the effective temperature of the system relaxes faster than the decay time of the skyrmions. Our results reveal a robust scenario for the generation of topological fluctuation states, potentially enabling their study in a wide variety of magnetic systems.