Electric coupling in scanning SQUID measurements

• Published in: arXiv.org
• Main Authors: Spanton, Eric M, Rosenberg, Aaron J, Wang, Yihua H, Kirtley, John R, Katmis, Ferhat, Jarillo-Herrero, Pablo, Moodera, Jagadeesh S, Moler, Kathryn A
• Format: Paper Journal Article
• Language: English
• Published: Ithaca Cornell University Library, arXiv.org 18.12.2015
• Subjects: Coupling; Electric potential; Ferromagnetism; Imaging; Magnetic domains; Magnetic fields; Magnetism; Physics - Mesoscale and Nanoscale Physics; Spatial distribution; Superconducting quantum interference devices
• ISSN: 2331-8422
• DOI: 10.48550/arxiv.1512.03373

Scanning SQUID is a local magnetometer which can image flux through its pickup loop due to DC magnetic fields (\(\Phi\)). Scanning SQUID can also measure a sample's magnetic response to an applied current (\(d\Phi/dI\)) or voltage (\(d\Phi/dV\)) using standard lock-in techniques. In this manuscript, we demonstrate that electric coupling between the scanning SQUID and a back gate-tuned, magnetic sample can lead to a gate-voltage dependent artifact when imaging \(d\Phi/dI\) or \(d\Phi/dV\). The electric coupling artifact results in \(d\Phi/dV\) and \(d\Phi/dI\) images which mimic the spatial variation of the static magnetic fields from the sample (e.g. ferromagnetic domains). In back-gated \(EuS/Bi_2Se_3\) bilayers, we show that the electric coupling effect is important, and is responsible for the reported signal from chiral currents in Y.H. Wang, et al. (DOI: 10.1126/science.aaa0508). Previous scanning SQUID current imaging experiments are unaffected by this artifact, as they are either on non-magnetic samples or the spatial distribution of magnetism does not match the features observed in \(d\Phi/dI\). In conclusion, \(d\Phi/dI\) or \(d\Phi/dV\) imaging of magnetic, back-gated samples should only be applied and interpreted with great caution.