Effect of helium ion irradiation on the tunneling behavior in niobium/aluminum-aluminum oxide/niobium josephson junctions

Tiantian Zhang, Cameron Kopas, Lei Yu, Ray Carpenter, Makram A. Qader, Mengchu Huang, Rakesh Singh, John Mardinly, Robin Cantor, John M. Rowell, Nathan Newman

Research output: Contribution to journalArticlepeer-review


The study of the effects of high-energy particle irradiation on trilayer Josephson junctions has allowed us to investigate the influence of defects and interfacial intermixing on the junction electrical characteristics. In this paper, we investigated the influence of 2-MeV helium ion irradiation with doses up to 5.25 × 1016cm2 on the tunneling behavior of Nb/Al-AlOxNb Josephson junctions. The modeling of the irradiation-induced chemical changes, combined with transmission-electron- microscopy characterization, indicates that over 2 nm of atomic intermixing occurs at all interfaces. Surprisingly, the quality of the tunneling characteristics is not significantly degraded, although some properties were affected: 1) The onset of the quasi-particle current characteristic of the electrodes' sum gap, Δ1 + Δ2, decreased from 2.8 to 2.6 mV; 2) the temperature onset of the Josephson current dropped from 9.2 K to 9.0 K; and 3) the normal resistance, Rn, increased by < , ∼20%. The dependence of the Josephson current on the magnetic field was not significantly altered. Modeling using proximity theory indicated that the irradiation-induced changes in the current-voltage (I-V) characteristics are likely due to an increased drop in the order parameter near the barrier interface as a result of a reduced mean free path in the Al proximity layer from Nb and O contamination.

Original languageEnglish (US)
Article number1101610
JournalIEEE Transactions on Applied Superconductivity
Issue number4
StatePublished - 2013


  • Josephson junction
  • particle irradiation
  • tunneling behavior

ASJC Scopus subject areas

  • Electronic, Optical and Magnetic Materials
  • Condensed Matter Physics
  • Electrical and Electronic Engineering


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