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Hybrid Nb/Al/Ba0.5K0.5Fe2As2 sandwich Josephson junctions

Authors:   Wanghao Tian, Yangyang Lv, Zuyu Xu1 Huili Zhang, Shixian Chen, Sining Dong, Jun Li , Yong-Lei Wang, Dieter Kölle, Reinhold Kleiner, Huabing Wang and Peiheng Wu

Supercond. Sci. Technol. 33 (2020) 025014

Abstract: We fabricated hybrid Josephson junctions between a Ba0.5K0.5Fe2As2 (BKFA) single crystal and the conventional superconductor Nb with normal metal Al as the barrier. An in situ process was used to create clean BKFA/Al/Nb interfaces. Current transport is along the c-axis of BKFA. The current–voltage characteristics are slightly hysteretic at low temperatures. Except for some features indicative of resonant modes the shape of the current–voltage characteristics can be well described by the resistively and capacitvely shunted junction (RCSJ) model, with a product of the Josephson critical current and the normal state resistance of the junction exceeding 180μV at low temperatures. The temperature dependence of the Josephson current is linear for temperatures down to 2K. Under 40GHz microwave irradiation integer Shapiro steps are observed. The power dependence of the Shapiro step-height is in good agreement with RCSJ simulations. Possible relations of our data with the symmetry of the superconducting order parameter of BKFA are discussed.

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