Magnetochiral Effects in Josephson Junctions and two-dimensional Josephson Junction Arrays

This thesis studies effects in Josephson junctions and two-dimensional arrays of Josephson junctions which arise in the presence of spin-orbit coupling and Zeeman fields. The experimental platform is a hybrid superconductor-semiconductor heterostructure. A near-surface indium arsenide quantum well is proximitized by an epitaxial film of superconducting aluminum. Josephson junctions are fabricated by selective etching of the superconductor. Measurements are performed at sub-Kelvin temperatures in a specialized dilution refrigerator setup. The thesis starts with an introduction to the theory of superconductor/normal conductor/superconductor (SNS) Josephson junctions and describes the novel effects which arise in the presence of spin-orbit coupling and Zeeman fields. The first experiment described in the thesis enables the measurement of both anomalous Josephson effect (also known as phi0-shift) and superconducting diode effect using an asymmetric superconducting quantum interference device (SQUID). Both effects can be tuned using a top gate which allows changing of the electron density in the Josephson junction. In the following chapters we study two-dimensional arrays of Josephson junctions (JJAs). One of the main discoveries is a novel type of vortex ratchet effect which arises in ballistic JJA devices. This magnetochiral effect is explained as a consequence of the anomalous phase shift. The inductance of Josephson vortices in two-dimensional arrays is studied in the following. We observe a characteristic behavior of vortex inductance as a function of frustration and observe non-reciprocal vortex inductance when applying in-plane magnetic fields. Finally, we study the insulating behavior of the two-dimensional JJAs. The JJAs are tuned to the insulating regime by depleting the electron gas in the junctions with a top gate electrode. In the insulating regime we observe critical threshold voltages caused by Coulomb blockade effects. Transport shows thermally activated behavior with an activation energy which depends both on the induced superconducting gap in the semiconductor and the electrostatic charging energy.