Al-Mn Transition Edge Sensors for Cosmic Microwave Background Polarimeters

Superconducting transition edge sensors (TES) require superconducting films with transition temperatures (T_c) and properties that can be tailored to the particular requirements of individual applications. We have been developing Al-Mn films with a tunable T_c. The addition of Mn to Al suppresses T_c, but does not significantly broaden the superconducting density of states of the Al. We can produce films with T_c from below 50 mK to 1.4 K through adjustment of the Mn concentration. Since this is a bulk effect, T_c is not as dependent on precise control of film thickness as in the standard bilayer approach for TESs. We have previously used Al-Mn to fabricate TES sensors for x-ray microcalorimeters 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.