Improved Modeling of Quasi-Static Thermal and Optical Response of Lumped-Element Aluminum Manganese KIDs

We report on the characterization of AlMn ki netic inductance detectors (KIDs) under consideration for use in the Next-generation Extended Wavelength-MUltiband Sub/millimeter Inductance Camera (NEW-MUSIC) [1] on the Leighton Chajnantor Telescope (LCT). NEW-MUSIC will cover 80-420 GHz, split into six spectral bands, with polarimetry. This broad spectral coverage will enable study of a range of scientific topics such as the accretion and feedback in galaxies and galaxy cluster evolution via the Sunyaev-Zeldovich effect, the transient synchrotron emission from the explosive deaths of massive stars and other time-domain phenomena, and dusty sources from low to high redshift (with polarization). Al KIDs have already been demonstrated for four bands centered at 150, 220, 275, and 350 GHz and will also be used for the 405 GHz band [1]. AlMn KIDs are a candidate for the 90 GHz band, as Al's pair-breaking energy is too high. However, AlMn has only barely been explored as a KID material. To this end, we first improved the modeling techniques used for KIDs within BCS theory by eliminating the use of analytical approximations for the expressions of the complex conductivity and found these changes reduced fit parameter degeneracy in the analysis of AlMn. Then, we tested the addition of a gap smearing parameter, a standard extension to BCS theory in use for materials for which the BCS model appears unsatisfactory, such as high kinetic inductance materials, and found that the model without this term is preferred by the data. We thus conclude that our AlMn resonators do not suffer from significant gap smearing. Finally, we observed optical response of the AlMn KIDs to mm-wave radiation and attempted to measure their optical efficiency, but the small response of these devices to optical loading at the operating temperatures attempted prevented us from obtaining meaningful constraints. Nevertheless, our data display AlMn's potential as a KID material for the 60–100 GHz frequency range.