Evidence of zero-point fluctuation of vortices in a very weakly pinned a-MoGe thin film

摘要

In a type-Ⅱ superconductor, the vortex core (VC) behaves like a normal metal. Consequently, the single-particle density of states in the VC of a conventional type-Ⅱ superconductor remains either flat or (for very clean single crystals) exhibits a peak at zero bias due to the formation of the Caroli-de Gennes-Matricon bound state inside the core. Here, we report an unusual observation from scanning tunneling spectroscopy measurements in a weakly pinned thin film of the conventional s-wave superconductor a-MoGe, namely, that a soft gap in the local density of states continues to exist even at the center of the VC. We ascribe this observation to rapid fluctuation of vortices about their mean position that blurs the boundary between the gapless normal core and the gapped superconducting region outside. Analyzing the data as a function of magnetic field, we show that the variation of fluctuation amplitude is consistent with quantum zero-point motion of vortices.