  The atomically clean surface of the iron-based superconductor FeTe0.55Se0.45
is investigated by low-temperature STM with different tip apex states. By
manipulating a single Fe atom onto the tip apex, signatures of the orbital
nature of the subsurface Fe layer of FeTe0.55Se0.45 can be identified. By
preparing a charged tip state, the intrinsic spatial inhomogeneity of the
chemical potential of FeTe0.55Se0.45 can be revealed. As a result, three
different types of vortex bound states originating from locally varying
topological properties of the FeTe0.55Se0.45 surface are observed by scanning
tunneling spectroscopy.
