Observation of the signatures of sub-resolution defects in two-dimensional superconductors with scanning SQUID

TL;DR

This paper demonstrates a scanning SQUID susceptometry technique with submicron resolution to detect and quantify localized defects in the superfluid density of two-dimensional superconductors, revealing sub-resolution features.

Contribution

It introduces a high-resolution imaging method to identify and analyze submicron defects in 2D superconductors, surpassing traditional mutual inductance limitations.

Findings

Localized susceptibility features correspond to suppressed superfluid density.

Features can be characterized by a single parameter indicating defect strength.

Method enables systematic defect detection in 2D superconducting systems.

Abstract

The diamagnetic susceptibility of a superconductor is directly related to its superfluid density. Mutual inductance is a highly sensitive method for characterizing thin films; however, in traditional mutual inductance measurements, the measured response is a non-trivial average over the area of the mutual inductance coils, which are typically of millimeter size. Here we image localized, isolated features in the diamagnetic susceptibility of {\delta}-doped SrTiO3, the 2-DES at the interface between LaAlO3 and SrTiO3, and Nb superconducting thin film systems using scanning superconducting quantum interference device susceptometry, with spatial resolution as fine as 0.7 {\mu}m. We show that these features can be modeled as locally suppressed superfluid density, with a single parameter that characterizes the strength of each feature. This method provides a systematic means of finding and quantifying submicron defects in two-dimensional superconductors.