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Subgap leakage and interface states in superconductor-insulator-superconductor tunnel junctions

Research output: Contribution to journalJournal article


  • Hyunsik Im
  • Yuri Pashkin
  • Yongmin Kim
  • T. F. Li
  • Kyooho Jung
  • O. Astafiev
  • J. S. Tsai
Journal publication date12/2010
JournalPhysica C: Superconductivity and its Applications
Number of pages2
Original languageEnglish


We use tunneling spectroscopy in Al and Nb based superconductor-insulator-superconductor (SIS) junctions to demonstrate the existence of metallic quasiparticle states at the interface of a superconducting electrode and an oxide layer, introducing a new method to directly evaluate the interface quasiparticle areal density of states. Current-voltage (I-V) characteristics typically observed in metal-insulator-superconductor (MIS) junctions are observed in the subgap voltage region. The turn-on voltage of the MIS-type leakage is found to be determined by the superconducting electrode with a smaller gap energy (Delta), and its magnitude depends on the nature of the interface. Our experiment suggests that the interface plays a key role in contributing to the subgap leakage influencing the performance of superconducting circuits.