We have found experimentally that the critical current of a square superconducting transition-edge sensor (TES) depends exponentially upon the side length L and the square root of the temperature T. As a consequence, the effective transition temperature Tc of the TES is current-dependent and at fixed current scales as 1/L^2. We also have found that the critical current can show clear Fraunhofer-like oscillations in an applied magnetic field, similar to those found in Josephson junctions. The observed behavior has a natural theoretical explanation in terms of longitudinal proximity effects if the TES is regarded as a weak link between superconducting leads. We have observed the proximity effect in these devices over extraordinarily long lengths exceeding 100 um.
@article{arxiv.0910.2451,
title = {Longitudinal Proximity Effects in Superconducting Transition-Edge Sensors},
author = {John E. Sadleir and Stephen J. Smith and Simon R. Bandler and James A. Chervenak and John R. Clem},
journal= {arXiv preprint arXiv:0910.2451},
year = {2014}
}