Numerical study of skyrmion-string dynamics

Magnetic skyrmion is a swirling emergent particle in two-dimensions characterized by the topological index called skyrmion number. The skyrmion in three dimensional chiral magnets forms a string, end points of which are monopole and antimonopole. This meandering one-dimensional object has many internal degrees of freedom including the rotation and breathing. The skyrmion string is driven by the current through the spin transfer torque effect, and the collision with the disorder induces a variety of phenomena. Here we show theoretically by the numerical simulation of a skyrmion string under current that the four distinct behaviors: (i) pinned string, (ii) depinned motion with the excitation of breathing mode, (iii) resonant excitation of breathing mode leading to the creation of monopole and antimonopole, and (iv) motional narrowing to recover the straight string, as the current density increases.