Al-Mn Transition Edge Sensors for Cosmic Microwave Background Polarimeters

Abstract

Superconducting transition edge sensors (TES) require superconducting films with transition temperatures (Tc)and properties that can be tailored to the particular requirements of individual applications. We have been developing Al-Mn films with a tunable Tc. The addition of Mn to Al suppresses Tc, but does not significantly broaden the superconducting density of states of the Al. We can produce films with Tc from below 50 mK to 1.4 K through adjustment of the Mn concentration. Since this is a bulk effect, Tc is not as dependent on precise control of film thickness as in the standard bi-layer approach for TESs. We have previously used Al-Mn to fabricate TES sensors for x-ray micro-calorimeters targeted for read out with time division SQUID multiplexing schemes. In this work, we explore the properties of Al-Mn in a regime well suited for frequency division multiplexing. We have also fabricated prototype Al-Mn cosmic microwave background polarimeters for the South Pole Telescope and will show initial measurements of these sensors.