Controlling $T_c$ of Iridium films using interfacial proximity effects

TL;DR

This paper demonstrates a simple method to suppress the critical temperature of iridium films using interfacial proximity effects with bilayers and trilayers, enabling better superconducting sensors.

Contribution

It introduces room-temperature deposition of Iridium-based multilayers to effectively lower $T_c$, improving fabrication of high-precision superconducting sensors.

Findings

Achieved $T_c$ suppression to 20-100 mK in Ir-based films.

Ir/Pt bilayers show tenfold higher impedance than Au/Ir/Au trilayers.

Method enables scalable, high-yield fabrication of low-$T_c$ superconducting films.

Abstract

High precision calorimetry using superconducting transition edge sensors requires the use of superconducting films with a suitable $T_c$, depending on the application. To advance high-precision macrocalorimetry, we require low-$T_c$ films that are easy to fabricate. A simple and effective way to suppress $T_c$ of superconducting Iridium through the proximity effect is demonstrated by using Ir/Pt bilayers as well as Au/Ir/Au trilayers. While Ir/Au films fabricated by applying heat to the substrate during Ir deposition have been used in the past for superconducting sensors, we present results of $T_c$ suppression on Iridium by deposition at room temperature in Au/Ir/Au trilayers and Ir/Pt bilayers in the range of $\sim$20-100~mK. Measurements of the relative impedance between the Ir/Pt bilayers and Au/Ir/Au trilayers fabricated show factor of $\sim$10 higher values in the Ir/Pt case. These new films could play a key role in the development of scalable superconducting transition edge sensors that require low-$T_c$ films to minimize heat capacity and maximize energy resolution, while keeping high-yield fabrication methods.