Vortex distributions near surface steps observed by scanning SQUID microscopy

Abstract

We have used a scanning superconducting quantum interference device microscope to image individual vortices near lithographically patterned surface steps in weak-pinning superconducting thin films of amorphous MoGe. The field-cooled vortex distributions are strongly influenced by the surface steps, with an enhanced vortex density along the thin side of the steps and a wide vortex-free region along the thick side of the steps. The surface steps induce orientational order that persists for many intervortex spacings away from the steps. We study the effects of surface step pinning for different magnetic-field strengths and step heights by analyzing the intervortex spacing and computing vortex correlation functions. For certain sample configurations, we are able to apply a Lorentz force to the vortices and observe an asymmetric vortex response near the surface steps. We discuss the interaction between a vortex and a surface step and consider possible mechanisms for generating the vortex distributions which we observe upon field cooling.

Flux penetration in a superconducting film partially capped with a conducting layer

“…In the last section, we discuss the flux penetration and interaction with a thickness step at the single vortex level as described by time-dependent Ginzburg-Landau simulations. The present study is also relevant for understanding the flux penetration in superconducting samples with terraces and thickness modulations [20], and it complements early investigations of static flux distributions near surface steps [21,22] and in mesoscopic samples [23].…”

Local superfluid densities probed via current-induced superconducting phase gradients

“…30 Furthermore, the inferred value of Ќ ͑B =0͒ is consistent with an estimate made using bulk penetration-depth and film-thickness data. 31 As Fig. 6 shows, the inverse period does indeed increase linearly, except at higher temperatures and fields.…”

Behavior of vortices near twin boundaries in underdoped Ba(Fe1−xCox)2As<

“…Sources of pinning locally reduce the free energy of a vortex that passes though them, resulting in improved critical current in samples with strong pinning [1,[6][7][8][9][10]. The various types of pinning sources, including oxygen vacancies, impurities, dislocations, extended columnar defects caused by irradiation, and others [1,[11][12][13][14][15], can be broadly categorized by the dimensionality of the pinning potentiality. One technologically important two-dimensional pinning source is grain boundaries, the boundaries between grains with different crystalline orientations [16].…”