Emergence of transient domain wall skyrmions after ultrafast demagnetization

Abstract

It is known that ultrafast laser pulses can be used to deterministically switch magnetization and createskyrmions; however, the deterministic creation of a single Néel skyrmion after ultrafast demagnetization remainsan open question. Here we show domain wall skyrmions also emerge in systems with broken inversion symmetryafter exposure to an ultrafast laser pulse, carrying an integer topological charge. While domain wall skyrmionsdo not appear in the relaxed state due to quick thermal decay following an Arrhenius law, they play a key role incontrolling the final skyrmion population through annihilations with skyrmions of opposite topological charge,with the resultant skyrmion states following a Poisson distribution. Using single-shot linearly polarized laserpulses, as well as a train of circularly polarized laser pulses, we show that when a high degree of disorder iscreated, the possibility of nucleating a single Néel skyrmion is accompanied by the possibility of nucleating askyrmion with domain wall skyrmion pair, which results in a self-annihilation collapse.