Anomalous dynamics of magnetic field-driven propagating magnetic domain walls.

Exact solutions of magnetic field-driven propagating topological solitons are found in the easy-plane phase of ferromagnetic spin-1 Bose-Einstein condensates, manifesting themselves as dark-soliton-like magnetic domain walls. Such solitons have two types: a low energy solution with positive inertial mass and a higher energy solution with negative inertial mass. Both types become identical at the maximum speed, a new speed bound that is different from speed limits set by the elementary excitations. The physical mass, which accounts for the number density dip, is negative for both types. In a finite one-dimensional system subject to a linear potential, the soliton undergoes oscillations, and transitions between the two types occurring at the maximum speed.