Superconducting Resonators with Niobium and $${\mathrm{YBa}_{2}\mathrm{Cu}_{3}O_{7-{\delta }}}$$YBa2Cu3O7-δ for Alpha-Particle Detectors

For high-energy particle detection at temperatures above 1 K, we investigated two superconducting films: niobium (Nb) and a high-temperature superconductor, namely $${\mathrm{YBa}}_2{\mathrm{Cu}}_3{\mathrm{O}}_{7-\delta }$$ (YBCO). Lumped element kinetic inductance detectors (LeKID) were fabricated using both the superconducting films. The alpha line (5.49 MeV emitted by Am-241) was irradiated from the top side of the devices. We observed only a very rapid signal from the YBCO-based LeKID, which cannot be attributed to a quasiparticle response because it is much faster than the resonator ring time ($$\sim 1\,{\upmu }$$s). Although the quality factor and noise level of the YBCO-based device were comparable to those of the Nb-base LeKID, the signal was suppressed because of the large gap energy and short quasiparticle lifetime. The performance of the Nb-based LeKID was consistent with expectations: The energy resolution was 17, and the decay time was approximately 1 $${\upmu }$$s. We distinguished between direct absorption events and phonon-mediated events.