Characterizing low-superconducting-gap materials for meV-scale dark matter detector fabrication*

Superconducting Quasiparticle-Amplifying Transmons (SQUATs) are a type of qubit-based sensor being developed by the Dark Matter and Quantum Information Science (DMQIS) group at SLAC. SQUATs can be utilized to detect photons and phonons with energy resolution comparable to the O(meV) superconducting band gap, Δ, associated with the photon/phonon absorber material. For a SQUAT whose sub-components are fabricated out of distinct materials, the differing, material-dependent band gaps can be exploited to preferentially funnel the photon- and phonon-induced quasiparticles into the lower-energy excited states available in the material with a smaller superconducting gap. Possible options for low-gap materials include Ti, Hf, and AlMn. However, there are additional practical considerations to be made when determining the promise of these candidate materials for use in SQUAT fabrication, namely, how the properties of their respective metal-oxides influence sensor behavior. In this talk, I will focus on my fabrication and film characterization work for SQUAT development, present preliminary results for Ti-based SQUATs, and outline future directions for this project.