Superconducting weak link generated on a linear array of substrate steps in ultrathin films of YBa2Cu3O7-x

TL;DR

This study demonstrates that substrate-induced steps in ultrathin YBCO films create superconducting weak links and flux-pinning centers, revealing new insights into flux dynamics and weak link behavior in high-temperature superconductors.

Contribution

It introduces a method to generate and analyze superconducting weak links using substrate steps in ultrathin YBCO films, highlighting their role in flux pinning and flux lattice matching effects.

Findings

Substrate steps produce superconducting weak links in YBCO films.

Faults act as one-dimensional flux-pinning centers.

Flux-flow resistivity shows a fine structure due to flux lattice matching.

Abstract

We have studied a three-unit-cell-thick YBa2Cu3O7-x (YBCO) superconducting film grown on a slightly vicinal SrTiO3 substrate that was polished from the (001) plane by a small miscut angle (less than 0.5 degrees). This produced, on its surface, a linear array of single-unit-cell-height steps with a period larger than 40 nm. A characteristic fault, with a displacement corresponding to one-third of the c-axis length of YBCO, is generated in the film on each substrate step, as observed by atomic force microscopy. Transport measurements with current flows parallel and perpendicular to the fault show that the fault serves as a superconducting weak link, as well as a unique one-dimensional flux-pinning center in an applied magnetic field. In addition, a characteristic fine structure is found in the flux-flow resistivity as a function of magnetic field, the origin of which may be ascribed to a matching effect between the periodically aligned faults and the flux lattice.