Imaging analysis of superconducting transition edge sensors for calorimeters

The superconducting-transition-edge temperature sensors (TES) for calorimeters operate in an intermediate state within normal-superconducting transition. The spatial profiles of a response to an x-ray microbeam exhibit that normal-superconducting phase separation occurs in an iridium TES with electrothermal feedback, as has been observed in many current-carrying conductors with self-heating. The resistive domain (normal region) in the 500 μm-square TES grows as applied bias voltage increases. This observation agrees reasonably well with a one-dimensional model of the self-heating. On the other hand, two-dimensional features are explained by nonuniform supercurrent distribution in the superconducting domain. These findings are important for developing detectors with a large detection area for energy dispersive x-ray spectroscopy.