Kavli Affiliate: Katja C. Nowack
| First 5 Authors: Samantha Walker, Austin Kaczmarek, Jason Austermann, Douglas Bennett, Shannon M. Duff
| Summary:
Significant advancements have been made in understanding the physics of
transition-edge sensors (TESs) over the past decade. However, key questions
remain, particularly a detailed understanding of the current-dependent
resistance of these detectors when biased within their superconducting
transition. We use scanning superconducting quantum interference device (SQUID)
microscopy (SSM) to image the local diamagnetic response of aluminum-manganese
alloy (Al-Mn) transition-edge sensors (TESs) near their critical temperature of
approximately 175 mK. By doing so, we gain insights into how the device
dimensions influence TES transition width, which in turn affects device
operation and informs optimal device design. Our images reveal that the Al-Mn
thin film near the niobium (Nb) leads exhibits an excess diamagnetic response
at temperatures several milli-Kelvin (mK) higher than the bulk of the film
farther from the contacts. A possible origin of this behavior is a longitudinal
proximity effect between the Nb and Al-Mn where the TES acts as a weak link
between superconducting leads. We discuss how this effect shapes the
temperature dependence of the resistance as the spacing between the leads
decreases. This work demonstrates that magnetic imaging with SSM is a powerful
tool for local characterization of superconducting detectors.
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