Berlin 2024 – wissenschaftliches Programm

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TT: Fachverband Tiefe Temperaturen

TT 6: Superconductivity: Tunnelling and Josephson Junctions I

TT 6.2: Vortrag

Montag, 18. März 2024, 09:45–10:00, H 3010

Shaping quantized current steps in Josephson junctions using tailored drives — •Fabian Kaap, Christoph Kissling, Victor Gaydamachenko, Asen Georgiev, Lukas Grünhaupt, and Sergey Lotkhov — Physikalisch-Technische Bundesanstalt, Bundesallee 100 38116, Deutschland Braunschweig

Recent experiments have confirmed predictions made nearly four decades ago about the existence of quantized current steps in Josephson junctions and superconducting nanowires - referred to as dual Shapiro steps. These steps, separated by 2ef, with e the elementary charge and f the frequency, hold potential for a novel current standard. To realize dual Shapiro steps, we embed a Al/AlO_x/Al dc-SQUID in a high-impedance environment made from granular aluminium and oxidized titanium. Demonstration of quantized current steps in the IV-curves is achieved with an external sinusoidal driving signal of frequencies up to 6 GHz, resulting in steps up to I=n × 2ef ≈ n × 2 nA. Using a sawtooth shaped driving signal instead, enhances the first dual Shapiro step at positive or negative currents while suppressing the opposite value step, contingent on the slope of the sawtooth signal. We compare the flatness of the enhanced current steps, as compared to the steps generated using the sinusoidal drive, by the peak values of the differential resistance R_diff=d U/d I and find an improvement by a factor of ∼ 2.

Keywords: Josephson effect; Shapiro steps; Metrology; Current standard