Meissner hole in pristine and proton-irradiated ${\mathrm{Ba}}_{1-x}{\mathrm{Rb}}_x{\mathrm{Fe}}_2{\mathrm{As}}_2$

We investigated the unstable interface between vortices and antivortices in single crystals of the iron-based superconductor (${\mathrm{Ba}}_{0.67}{\mathrm{Rb}}_{0.33}$)${\mathrm{Fe}}_2{\mathrm{As}}_2$ ($T_c\sim 37.6$ K). This interface, also known as the Meissner hole, was captured with magneto-optical imaging in both a pristine crystal and one with artificial point defects. We confirmed the presence of local excess current flowing along the interface. The dynamics of such an interface qualitatively follows the prediction of the critical state model, accompanied by a finite relaxation rate of magnetization. However, quantitatively, the local relaxation of the Meissner hole can be much faster than that of magnetization due to local deformation of the excess current.