  We have studied the superconducting Si(111)-(root7xroot3)-In surface using a
3He-based low-temperature scanning tunneling microscope (STM). Zero-bias
conductance (ZBC) images taken over a large surface area reveal that vortices
are trapped at atomic steps after magnetic fields are applied. The crossover
behavior from Pearl to Josephson vortices is clearly identified from their
elongated shapes along the steps and significant recovery of superconductivity
within the cores. Our numerical calculations combined with experiments clarify
that these characteristic features are determined by the relative strength of
the interterrace Josephson coupling at the atomic step.
