We have studied the superconducting $\mathrm{Si}(111)\text{−}(\sqrt{7}\times \sqrt{3})\text{−}\mathrm{In}$ surface using a ${}^3\mathrm{He}$-based low-temperature scanning tunneling microscope. Zero-bias conductance 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.

• Received 19 March 2014

DOI:https://doi.org/10.1103/PhysRevLett.113.247004