Electric coupling in scanning SQUID measurements

Abstract

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 $EuS/B{i}_{2}S{e}_3$ 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.

This is a comment on Y.H. Wang, et al. (DOI: 10.1126/science.aaa0508), which has been retracted (DOI: 10.1126/science.350.6267.1482-a)

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Cited by in corpus (5)

• Opportunities in topological insulator devices
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• Electrically tunable multi-terminal SQUID-on-tip
• Local optical control of ferromagnetism and chemical potential in a topological insulator
• Chiral and Non-Chiral Edge States in Quantum Hall Systems with Charge Density Modulation