Regensburg 2019 – scientific programme
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TT: Fachverband Tiefe Temperaturen
TT 55: Superconductivity: Tunneling and Josephson Junctions
TT 55.5: Talk
Thursday, April 4, 2019, 10:30–10:45, H23
Scanning tunneling spectroscopy of superconducting Granular Aluminium — •Tim Storbeck, Fang Yang, Ioan Pop, and Wulf Wulfhekel — Karlsruhe Institut of Technology
Granular Al films are of high interest for quantum superconducting circuit design due to their large kinetic inductance and low intrinsic dissipation. Interestingly, it has been known for several decades that Tc can be increased by a factor more than 2 in granular Al compared to bulk Al. The enhancement of Tc has been attributed to microscopic mechanisms involving electron quantization and Kubo spins, however, the exact mechanisms are still debated. We report the measurement of scanning tunneling spectroscopy of granular Al films on Nb-doped SrTiO3 in ultra-high vacuum at 30mK. We observed both superconducting and insulating grains in the same samples. The local single electron tunneling between the tip and the Al grains show rich features at energy scales from 1 eV down to 0.1 meV. The size of the gap in superconducting grains, in the range of 0.28-0.32 meV, agrees with previously reported values for similar films. We also observed signatures of in-gap states, hinting at unpaired electrons on the grains.