A hot-electron microcalorimeter for X-ray detection using a superconducting transition edge sensor with electrothermal feedback

We investigate a hot-electron microcalorimeter for X-ray detection. The X-ray absorber consists of a normal metal film in thermal and electrical contact with a superconducting transition-edge sensor. The sensor is formed by a proximity-effect bilayer of aluminum and silver, with a sharp superconducting transition near 100 mK. Energy from X-rays absorbed in the normal film is removed by a reduction of the Joule heating in the proximity bilayer due to electrothermal feedback and measured using a SQUID. The feedback mode of operation allows the measurement of incident energy with no free parameters and should lead to improvement in detector resolution over existing hot-electron microcalorimeters.