Driving the field-free Josephson diode effect using Kagome Mott insulator barriers

TL;DR

This paper demonstrates that the Josephson diode effect in quantum material Josephson junctions can be controlled by the correlation strength of Kagome Mott insulator barriers, revealing a correlation-driven mechanism for non-reciprocal superconductivity.

Contribution

It introduces a method to tune the Josephson diode effect using correlated Kagome insulators with varying U/t, showing correlation strength influences the effect.

Findings

JDE decreases with increasing U/t in Kagome insulator barriers.

Nb3Cl8 exhibits ~48% JDE efficiency, Nb3Br8 ~6%, Nb3I8 no discernible JDE.

Correlation in insulators drives the field-free Josephson diode effect.

Abstract

Josephson junctions (JJs), devices consisting of two superconductors separated by a barrier, are of great technological importance, being a cornerstone of quantum information processing. Classical understanding of superconductor-insulator-superconductor JJs is that conventional insulator's properties, other than magnetism, do not significantly influence the junction's behavior. However, recent work on quantum material (QM) JJs - using Mott insulator Nb3Br8 - resulted in magnetic field-free non-reciprocal superconductivity, termed the Josephson diode effect (JDE), implying the QM's intrinsic properties can modulate superconductivity in non-trivial ways. To date, the underlying mechanism and dependence of the JDE on correlation strength (U/t) has not been elucidated. Here we fabricate QMJJs using correlated Kagome insulators with varying U/t, Nb3X8 (X=Cl, Br, I), observing a decreasing trend of the field-free JDE with Nb3Cl8 reaching ~48% efficiency, Nb3Br8 ~6%, and Nb3I8 having no discernible JDE, matching the trend of decreasing U/t from Cl to I and suggesting correlation in insulators drives the field-free JDE.