Excitation spectrum of Josephson vortices on surface superconductor

Abstract

Motivated by recent discovery of superconductivity in monatomic In layer on silicon surfaces and scanning tunneling microscopy and spectroscopy (STM/STS) measurement, we study the excitation spectrum of vortex in a two-dimensional superconductor. According to the STM/STS measurements, the zero bias conductance (ZBC) for the vortices trapped at atomic steps has an anisotropic shape. In order to understand the experimental results, we study the local density of states (LDOS) as a function of strength of hopping integral at atomic steps. Our analysis is based on the self-consistent solution of the Bogoliubov-de Gennes equation coupled with a gap equation. The amplitude of the order parameter is restored at the vortex core and the phase winding becomes anisotropic with decreasing the hopping strength at atomic steps. The zero energy LDOS stretches along the step and the intensity decreases associated with the deformation of the order parameter. By comparing the theoretical results with experiments, we conclude Josephson vortices in 2D superconductivity have been observed.