Turbulent Structure and Characterization of ‘11’-type Iron-based Superconductors by Magneto-optical Imaging

Magneto-optical imaging is employed to investigate the vortex penetration modes in ‘11’-type iron-based superconductors (IBSs) Fe(Te 0.6 Se 0.4 ) and FeSe single crystals. In Fe(Te 0.6 Se 0.4 ), vortices penetrate mostly homogeneously from all edges, forming an unstable turbulent interface with pre-existing anti-vortices, where ‘Meissner hole’ emerges as those have been reported in ‘122’-type IBSs. In FeSe, however, the penetration is restricted to numerous mesoscopic stripe-like regions. Further experiments revealed an inhomogeneous vortex propagation pattern, where vortices are most likely to be channeled along the twin boundaries.