Geometric dependence of critical current magnitude and nonreciprocity in planar Josephson junctions

TL;DR

This study investigates how the geometry and electrostatic gating of planar Josephson junctions influence their critical current and superconducting diode effect, revealing dependencies on contact width, magnetic field, and underlying physical mechanisms.

Contribution

It provides new insights into the geometric and electrostatic control of the superconducting diode effect in planar Josephson junctions, highlighting the roles of contact width and induced coherence length.

Findings

Critical current and diode efficiency increase with contact width.

Maximum diode efficiency occurs at a field inversely related to contact width.

Gate voltage significantly affects the critical current and optimal field.

Abstract

Planar Josephson junctions in a magnetic field exhibit the superconducting diode effect, by which the critical current magnitude depends on the polarity of the transport current. A number of different mechanisms for the effect have been proposed.Here, we study symmetric, T-shaped planar Josephson junctions with semiconducting weak links in an in-plane magnetic field perpendicular to an applied current bias. In particular, we vary the longitudinal width (i.e.\ parallel to the current) of the superconducting contacts and the voltage of an electrostatic gate. We observe an increase in both critical current and diode efficiency with increasing contact width and relate the critical current behavior to the induced coherence length of the Andreev bound states that mediate the supercurrent flow through the junction. We further observe a linear trend, with respect to inverse contact width, of the field at which the diode efficiency is maximized, which saturates as the contact width becomes large compared to the coherence length. The smaller field at which the critical current is maximized additionally exhibits a strong gate dependence. We interpret these observations in the context of multiple underlying mechanisms, including spin--orbit coupling and orbital effects.