Direct Imaging of the Proximity Effect in S-S'-S Devices

The superconducting proximity effect occurs when a superconductor (S) is placed in contact with a non-superconductor (N). At the S-N interface, the N-region inherits a weak form of superconductivity and the superconductivity in the S-region becomes degraded. Similarly, placing a superconductor S in contact with a superconductor S’ with a significantly lower transition temperature (Tc’ <<Tc), the S’ region experiences enhanced superconductivity near the S-S’ interface. In this work, we use scanning superconducting quantum interference device (SQUID) microscopy to locally detect the diamagnetic response associated with superconductivity, enabling us to directly image the proximity effect in Nb\Al-Mn\Nb S-S’-S devices. These devices form the basis of a transition edge sensor (TES) bolometer, widely used as the sensing component in millimeter-wave astronomy telescopes for cosmological observations. By increasing the temperature above Tc’, we probe the proximity effect as the system transitions from a S-S’-S to a S-N-S device. We find that a diamagnetic response, and therefore superconductivity, persists in the Al-Mn region near the interface well above its nominal Tc’. Additionally, our data suggests that the spatial extent of the proximity effect is long-ranged, extending up to tens of microns.