Imaging the Superconducting Proximity Effect in S-S'-S Transition Edge Sensors

TL;DR

This study uses scanning SQUID susceptometry to directly image and analyze the spatial proximity effects in superconducting transition edge sensors, revealing how local transition temperatures are influenced by neighboring regions and providing insights for device optimization.

Contribution

It provides the first direct spatial imaging of proximity effects in TES devices, combining experimental measurements with Ginzburg Landau and Usadel modeling to understand superconducting state control.

Findings

Long-range proximity coupling over tens of micrometers

Local transition temperature modulation by neighboring regions

Quantitative agreement with theoretical models

Abstract

Proximity effects at superconducting interfaces, between different superconductors (S-S') or between superconductors and normal metals (S-N), are fundamental to the performance of superconducting electronics, yet only few experiments have directly probed the spatial structure of proximity effects within a device. This is particularly relevant for transition edge sensors (TESs), where the interplay of direct and inverse proximity effects governs detector sensitivity. Here, we use scanning superconducting interference device (SQUID) susceptometry to directly image the local diamagnetic response in functional S-S'-S TES structures. We resolve long range proximity coupling extending over tens of micrometers, revealing that the local transition temperature is dramatically tuned by neighboring regions, being either enhanced by superconducting (S) leads or suppressed by normal metal (N) contacts. Our observations are quantitatively supported by Ginzburg Landau modeling of the device geometry and calculations of the temperature dependent diamagnetism based on self-consistent Usadel equations. By providing spatially resolved measurements of the interplay of proximity effects in TES devices, this work establishes a framework for understanding and controlling superconducting states in heterogeneous superconducting structures.