Vertical Josephson field-effect transistors based on black phosphorus

Authors: Zuyu Xu, Wei Chen, Junwei Huang, Wanghao Tian, Shixian Chen, Wencheng Yue, Tianyuan Chi, Yang-Yang Lyu, Hancong Sun, Yong-Lei Wang, Guozhu Sun, Jian Chen, Biaobing Jin, Song-Lin Li, Hongtao Yuan, Jun Li, Dieter Koelle, Reinhold Kleiner, Huabing Wang and Peiheng Wu

Appl. Phys. Lett. 119, 072601 (2021)

Abstract: The gate-tunable Josephson junction, generally achieved in planar Josephson field-effect transistors (JoFETs), is a key element for the applications of superconducting devices. At present, the performance of these systems with planar JoFETs is often impeded by the large channel length, which, at best, lies in the range of tens of nanometers. In contrast, the channel length in vertical junctions can be easily scaled down to nano-scale to realize the strong Josephson coupling. However, the vertical junctions are believed to be insensitive to the field-effect due to the atomic screening of electric fields in metals. Here, we report on a novel realization of few-layer black phosphorus (BP)-based vertical JoFETs using an electric-double-layer configuration. In transport experiments, using junctions of different shape, superconducting quantum interference device-like magnetic diffraction patterns of the junction critical current and anomalous Shapiro steps on current voltage characteristics are observed, strongly indicating that the critical current density in the junctions is highly inhomogeneous and peaked at the edges or even near the junction corners. The electric-field tunability of the Josephson coupling could be attributed to the edge- or cornerdominated supercurrent density profile combining with the carrier diffusivity in the few-layer BP. The ability to control the vertical
Josephson coupling provides us with new opportunities to study high-performance and high-temperature superconducting Josephson fieldeffect
transistors operating on an atomic-scale channel length.

DOI: https://doi.org/10.1063/5.0061999