Dresden 2026 – scientific programme

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TT: Fachverband Tiefe Temperaturen

TT 22: Superconductivity – Poster I

TT 22.8: Poster

Monday, March 9, 2026, 18:00–20:00, P1

Coulomb blockade in ultrasmall step-edge junctions made of granular aluminum — •Sergey Lotkhov and Lukas Grünhaupt — Physikalisch-Technische Bundesanstalt, Bundesallee 100, 38116 Braunschweig

We developed a fabrication routine and implemented a Coulomb blockade transistor with two step-edge junctions made of granular aluminum (grAl) superconductive film. Our process neither involves widely-used shadow-evaporated overlaps, nor the surface oxidation of aluminum for creating the tunnel barriers. This technique enables multijunction single-charge circuitry free of stray replicas. At low temperatures, the transistor exhibited a typical periodic structure of Coulomb diamonds adjacent to the superconducting voltage gap of grAl, both varying under experimental conditions. The gap was found to depend weakly on the transversal magnetic field up to at least 2 Tesla, which we explain by the microstructure of the superconductive grAl film. Furthermore, the charging effects persisted unaffected across the superconducting transistion of grAl, thus supporting a simple, single-electron tunneling picture of the Coulomb effects observed.

Keywords: granular aluminum; Coulomb blockade; single-electron transistor; nanofabrication; tunnel junctions