SKM 2021 – wissenschaftliches Programm

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TT: Fachverband Tiefe Temperaturen

TT 1: Focus Session: Disordered and Granular Superconductors: Fundamentals and Applications in Quantum Technology I

TT 1.7: Vortrag

Montag, 27. September 2021, 12:15–12:30, H6

Decoupling of the Quasiparticle Number and Lifetime in a Disordered Superconductor Probed by Quasiparticle Fluctuation Measurements — •Steven A. H. de Rooij^1,2, Kevin Kouwenhoven^1,2, Jochem J. A. Baselmans^1,2, Vignesh Murugesan², David J. Thoen^1,3, and Pieter J. de Visser² — ¹SRON - Netherlands Institute for Space Research, Leiden, The Netherlands — ²Department of Microelectronics, Delft University of Technology, The Netherlands — ³Kavli Institute of NanoScience, Delft University of Technology, Delft, The Netherlands

In a superconductor, the number of quasiparticles (N_qp) decreases exponentially when lowering the temperature, while the quasiparticle lifetime increases, i.e. τ_qp∼ 1/N_qp. Measuring quasiparticle fluctuations, induced by thermal fluctuations, give access to both τ_qp and N_qp. In disordered superconductors, these fundamental quasiparticle properties have hardly been studied, although these materials are widely applied in high kinetic inductance quantum circuits and kinetic inductance detectors. We measured quasiparticle fluctuations in the disordered superconductor β-Ta, embedded in a NbTiN microwave resonator, probing both the dissipation (i.e. quasiparticles) and kinetic inductance (i.e. Cooper-pairs). We observe a non-conventional temperature dependence of τ_qp, i.e. τ_qp 1/N_qp, which results in a strong reduction of the quasiparticle fluctuations with decreasing temperature. This behavior is similar to that of the conventional superconductor Al, where we relate it to quasiparticle trapping [arXiv:2103.04777], which may also play a role in disordered superconductors.