Controlling T c of iridium films using the proximity effect

Abstract

A superconducting Transition-Edge Sensor (TES) with low-T c is essential in a high resolution calorimetric detection. With a motivation of developing sensitive calorimeters for applications in cryogenic neutrinoless double beta decay searches, we have been investigating methods to reduce the T c of an Ir film down to 20 mK. Utilizing the proximity effect between a superconductor and a normal metal, we found two room temperature fabrication recipes of making Ir-based low-T c films. In the first approach, an Ir film sandwiched between two Au films, a Au/Ir/Au trilayer, has a tunable T c in the range of 20-100 mK depending on the relative thicknesses. In the second approach, a paramagnetic Pt thin film is used to create Ir/Pt bilayer with a tunable T c in the same range. We present detailed study of fabrication and characterization of Ir-based low-T c films, and compare the experimental results to theoretical models. We show that Ir-based films with predictable and reproducible critical temperature can be consistently fabricated for use in large scale detector applications.

Light Dark Matter Detection with Hydrogen-rich Crystals and Low-Tc TES Detectors

“…For a reduction of TES heat capacity, it makes sense to fabricate thin Ir-based bilayers for low-T c TES. With the proximity models and materials data in reference [127], as well as the extracted electron interface transparencies (0.094 between Ir and Pt and 0.105 between Ir and Au) and electron spin relaxation time in Pt (0.076 ns) in reference [126], we show recipes for thin Ir/Pt and Ir/Au bilayers with tunable low-T c in Fig. 5.…”

“…On the other hand, a low-T c TES utilizing proximity effect is an alternative technical path forward. It was demonstrated that Ir-based proximity films, which include both Ir/Pt bilayers and Au/Ir/Au trilayers [126] sputtered at room temperature, have tunable T c down to 20 mK. The measured Ir-based bilayers and trilayers [126] are thick.…”

“…It was demonstrated that Ir-based proximity films, which include both Ir/Pt bilayers and Au/Ir/Au trilayers [126] sputtered at room temperature, have tunable T c down to 20 mK. The measured Ir-based bilayers and trilayers [126] are thick. This is because all of them used 100 nm thick Ir films.…”

Development of Cryogenic Detectors for Neutrinoless Double Beta Decay Searches with CUORE and CUPID

“…In the last ten years, different isotopes (see Figure 2) and approaches were investigated for CUPID. Background rejection with scintillation, Cherenkov radiation, ionization, and pulse-shape discrimination were evaluated, and novel materials and sensor technologies were tested [58,59]. The activities carried out over the last years to design a next-generation 0νββ bolometric experiment are briefly summarized here, divided according to the isotope under investigation.…”

“…Such an effect is due to the relatively short 100 Mo 2νββ half-life, combined with its high isotopic abundance, and the slow response time of the bolometric detectors. New methods are being developed in order to study and tackle this issue [87], and a further improvement of the pile-up rejection is expected to be achieved by combining a faster sensor (100 µs) with new analysis techniques based on Principal Component Analysis and Single Value Decomposition [58,88,89]. The exact evaluation of the expected pile-up rejection efficiency is underway and will be presented in future works of the CUPID collaboration.…”