Dynamic transition and Galilean relativity of current-driven skyrmions

TL;DR

This paper investigates the emergent electrodynamics of current-driven skyrmion lattices in Gd₂PdSi₃, demonstrating dynamic transitions from pinned to flow regimes and showing that Galilean relativity can be restored in the flow regime, affecting the topological Hall effect.

Contribution

It reveals the dynamic transition of skyrmion lattice motion and demonstrates the recovery of Galilean relativity in the flow regime, impacting the understanding of emergent electrodynamics in skyrmion systems.

Findings

SkL transitions from pinned to creep to flow regimes with increasing current.

The topological Hall effect is suppressed in the flow regime.

Large THE voltages enable real-time SkL velocity measurements.

Abstract

The coupling of conduction electrons and magnetic textures leads to quantum transport phenomena described by the language of emergent electromagnetic fields [1-3]. For magnetic skyrmions, spin-swirling particle-like objects, an emergent magnetic field is produced by their topological winding [4-6], resulting in the conduction electrons exhibiting the topological Hall effect (THE) [7]. When the skyrmion lattice (SkL) acquires a drift velocity under conduction electron flow, an emergent electric field is also generated [8,9]. The resulting emergent electrodynamics dictate the magnitude of the THE via the relative motion of SkL and conduction electrons. Here, we report the emergent electrodynamics induced by SkL motion in Gd$_2$PdSi$_3$, facilitated by its giant THE [10,11]. With increasing current excitation, we observe the dynamic transition of the SkL motion from the pinned to creep regime and finally to the flow regime, where the THE is totally suppressed. We argue that the Galilean relativity required for the total cancellation of the THE can be generically recovered in the flow regime, even in complex multiband systems such as the present compound. Moreover, the observed THE voltages are large enough to enable real-time measurement of the SkL velocity-current profile, which reveals the inertial-like motion of the SkL in the creep regime, appearing as current-hysteretic behavior of the skyrmion velocity.