Gate-defined superconducting channel in magic-angle twisted bilayer graphene

Abstract

Magic-angle twisted bilayer graphene (MATBG) combines in one single material different phases such as insulating, metallic, and superconducting. These phases and their in situ tunability make MATBG an important platform for the fabrication of superconducting devices. We realize a split-gate-defined geometry which enables us to tune the width of a superconducting channel formed in MATBG. We observe a smooth transition from superconductivity to highly resistive transport by progressively reducing the channel width using the split gates or by reducing the density in the channel. Using the gate-defined constriction, we control the flow of the supercurrent, either guiding it through the constriction or throughout the whole device or even blocking its passage completely. This serves as a foundation for developing quantum constriction devices such as superconducting quantum point contacts, quantum dots, and Cooper-pair boxes in MATBG.