Vertical Nb/TiOx/Nb Josephson Junctions Controlled by In-Plane Hot-Electron Injection
Authors: Zuyu Xu, Shixian Chen, Wanghao Tian, Zaidong Qi, Wencheng Yue, Hongmei Du, Hancong Sun, Caihong Zhang, Jingbo Wu, Sining Dong, Yong-Lei Wang, Weiwei Xu, Biaobing Jin, Jian Chen, Guozhu Sun, Dieter Koelle, Reinhold Kleiner, Huabing Wang and Peiheng Wu
Phys. Rev. Applied (2020) 14, 024008
Abstract: We fabricate vertical Nb/TiOx/Nb Josephson junctions where the TiOx layer is mostly metallic but has a high-resistance interface with the top Nb electrode. Thus, the junctions are in essence of the superconductor–insulator–normal-metal–superconductor type. The TiOx layer extends beyond the junction area and allows one to send an in-plane current through the normal-metal layer of the junction. We investigate and analyze dc properties (critical current, current-voltage characteristics) as well as the behavior of the junctions in external microwave fields. We find a strong dependence of all properties on the voltage Vi applied across the TiOx lead. The dependence on Vi can be mapped to the dependence of the junction parameters on the bath temperature T, when Vi is converted to an effective electronic temperature via Te=[T2+(aVi)2]1/2, with a=3.14K/mV. This relation was used before in the context of a metallic nanowire contacted by superconducting electrodes. While the geometry of our TiOx layer is far from that of a nanowire, the scaling works perfectly well for all experimental data. Our data also indicate that the electronic temperature is homogeneous throughout the junction area, a result that is unexpected for the large junction sizes we use. The device allows easy and relatively fast in situ manipulation of the junction parameters.