Superconductivity in 2D Gate-Tunable Heterostructures

Abstract

Electronic states confined to 2-dimensions (2Ds) display a rich array of phenomena notfound in their 3-dimensional counterparts. In 2D superconductors, the reduced dimen- sionality enhances the role of fluctuations, giving rise to Berezinskii–Kosterlitz–Thouless (BKT) transitions and rich vortex phenomena with a strong dependence on the su- perfluid density. Remarkably, the dilute 2D superfluid can be modified by an electric field, allowing for the study of density and disorder driven quantum phase transitions. Furthermore, this offers a promising route to field-effect superconducting electronics. In this dissertation, I will present measurements of novel devices in the 2D super- conducting state at the interface of the complex oxide KTaO3. Explicit electrostatic modification of the superconducting state is demonstrated by a total suppression of supercurrent, before revealing the interplay with a Coulomb blockade. The influence of charging energy in the Coulomb blockade regime results in an unusual periodic supercurrent and quantum dot behaviour under an applied magnetic field. The neg- ligible magnetic screening of 2D superconductivity forms a critical state of vortex matter which results in the observation of quantum tunneling of individual vortices from pinning sites in the device. Analysis of the tunneling rate suggests overdamped tunneling, as may be expected for a topological defect consisting of many electrons. These results demonstrate the rich array of quantum phases that can be realised in a single heterostructure, and furthermore inform the development of quantum devices and fundamental studies of quantum dynamics.