Controlling $T_c$ of Iridium films using interfacial proximity effects
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Open Access Publications from the University of California

Controlling $T_c$ of Iridium films using interfacial proximity effects

  • Author(s): Hennings-Yeomans, R
  • Chang, CL
  • Ding, J
  • Drobizhev, A
  • Fujikawa, BK
  • Han, S
  • Karapetrov, G
  • Kolomensky, YG
  • Novosad, V
  • O'Donnell, T
  • Ouellet, JL
  • Pearson, J
  • Polakovic, T
  • Reggio, D
  • Schmidt, B
  • Sheff, B
  • Smith, RJ
  • Wang, G
  • Welliver, B
  • Yefremenko, VG
  • et al.

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.

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