Driven skyrmions and dynamical transitions in chiral magnets

TL;DR

This paper investigates the behavior of skyrmions in chiral magnets under spin-polarized currents, revealing dynamic creation, deformation, and instability transitions that lead to a chiral liquid state, with observable signatures in transport measurements.

Contribution

It introduces a comprehensive dynamic phase diagram for skyrmions under current, highlighting the mechanisms of their creation, deformation, and transition to a chiral liquid state in chiral magnets.

Findings

Skyrmions are dynamically created from ferromagnetic states at high currents.

Spin wave spectrum becomes gapless, leading to skyrmion instability.

Transport measurements show jumps and hysteresis corresponding to phase transitions.

Abstract

We study the dynamics of skyrmions in chiral magnets in the presence of a spin polarized current. The motion of skyrmions in the ferromagnetic background excites spin waves and contributes to additional damping. At a large current, the spin wave spectrum becomes gapless and skyrmions are created dynamically from the ferromagnetic state. At an even higher current, these skyrmions are strongly deformed due to the damping and become unstable at a threshold current, leading to a chiral liquid. We show how skyrmions can be created by increasing the current in the magnetic spiral state. We then construct a dynamic phase diagram for a chiral magnet with a current. The instability transitions between different states can be observed as experimentally clear signatures in the transport measurements, such as jumps and hysteresis.