Enhanced quasiparticle lifetime in a superconductor by selective blocking of recombination phonons with a phononic crystal

K. Rostem, P. J. de Visser, and E. J. Wollack
Phys. Rev. B 98, 014522 – Published 27 July 2018

Abstract

When quasiparticles in a BCS superconductor recombine into Cooper pairs, phonons are emitted within a narrow band of energies above the pairing energy at 2Δ. We show that a phonon band gap restricting the escape of recombination phonons from a superconductor can increase the quasiparticle recombination lifetime by more than an order of magnitude. A phonon band gap can be realized and matched to the recombination energy with a phononic crystal, a periodically patterned dielectric membrane. We discuss in detail the nonequilibrium quasiparticle and phonon distributions that arise in a superconductor due to a phonon band gap and a pair-breaking photon signal. Although intrinsically a nonequilibrium effect, the lifetime enhancement in the small-signal regime is remarkably similar to an estimate from an equilibrium formulation. The equilibrium estimate closely follows exp(Ωbg/kBTb), where Ωbg is the phonon band gap energy bandwidth above 2Δ and Tb is the phonon bath temperature of the coupled electron-phonon system. We discuss the impact of a phononic band gap on the performance of a superconducting circuit element and propose a microwave resonator to measure the enhancement in the quasiparticle lifetime.

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  • Received 18 May 2018

DOI:https://doi.org/10.1103/PhysRevB.98.014522

©2018 American Physical Society

Physics Subject Headings (PhySH)

Condensed Matter, Materials & Applied Physics

Authors & Affiliations

K. Rostem1,*, P. J. de Visser2, and E. J. Wollack1

  • 1NASA Goddard Space Flight Center, 8800 Greenbelt Road, Greenbelt, Maryland 20771, USA
  • 2SRON, Netherlands Institute for Space Research, Sorbonnelaan 2, 3584 CA, Utrecht, The Netherlands

  • *karwan.rostem@nasa.gov

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Issue

Vol. 98, Iss. 1 — 1 July 2018

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