Normal metal - superconductor decoupling as a source of thermal fluctuation noise in transition-edge sensors

TL;DR

This paper investigates the excess noise in superconducting transition-edge sensors, attributing it to thermal decoupling between normal and superconducting regions, and proposes a thermal model explaining the observed phenomena.

Contribution

The study introduces a thermal model with three bodies to explain excess noise in TES, highlighting the role of high-frequency thermal decoupling within the device.

Findings

Most noise features explained by a three-body thermal model

Thermal decoupling causes excess noise and impedance features

Heat capacity jump at Tc is smaller than BCS prediction

Abstract

We have studied the origin of excess noise in superconducting transition-edge sensors (TES) with several different detector designs. We show that most of the observed noise and complex impedance features can be explained by a thermal model consisting of three bodies. We suggest that one of the thermal blocks and the corresponding thermal fluctuation noise arises due to the high-frequency thermal decoupling of the normal and superconducting phase regions inside the TES film. Our results are also consistent with the prediction that in thin bilayer proximitized superconductors, the jump in heat capacity at the critical temperature is smaller than the universal BCS theory result.