Control and manipulation of superconducting vortex lattices from nano to mesoscales*

Single and few vortex manipulation opens a pathway to understand vortex properties and to tailor their dynamics to prospective applications in quantum computing. We will discuss two experiments using scanning tunneling microscopy (STM) which demonstrate direct control over vortex positions in FeSe superconductor. First, we observed that the twin boundary in the FeSe superconductor traps a relatively high density of vortices and acts as a barrier that aligns the vortices on the terrace parallel to the twin boundary. The alignment effect causes various phases of vortex lattice structures such as rectangular and one-dimensional vortex lattices – both with ordering qualitatively different from the commonly observed vortex glass [2]. Second, we found that the vortex shape can be controllably varied with the imaging conditions in STM, particularly at the extreme limit of very large local current density. We attribute the observations as direct evidence of vortex manipulation, by contrasting the behaviors of various types of vortices in proximity to twin boundaries on FeSe. Altogether we suggest that precise control over the high tunneling current, combined with specific structural topological defects, can translate into an effective strategy for vortex manipulation approach without destruction of the superconducting state, enabling STM to become a quantitative nanoscale probe of vortex dynamics and a platform to explore vortex manipulation in the context of topological quantum computing.