Supercurrent spin Hall effect enabled nanopillar Josephson diodes

TL;DR

This paper demonstrates a new approach to achieve higher efficiency Josephson diodes by utilizing the supercurrent spin-Hall effect in a heavy metal barrier, enabling non-reciprocal supercurrent at higher temperatures.

Contribution

It introduces intrinsic spin-orbit coupling in a heavy metal Josephson barrier to induce non-reciprocity, surpassing previous external field-based methods.

Findings

Achieved Josephson diode efficiencies up to 17%

Demonstrated non-reciprocal supercurrent above liquid helium temperature

Realized net spin segregation via supercurrent spin-Hall effect in Pt barrier

Abstract

In the recent years it has been possible to achieve diode-like, non-reciprocal current-voltage response in Josephson junctions, despite the intrinsic symmetry of the Josephson effect itself. This is typically achieved by incorporating Rashba spin-orbit coupling into the Josephson junction as a strong inversion symmetry breaking component, and external magnetic field as a tuneable time-reversal symmetry breaking component. However, the efficiencies of the external field tuneable Josephson-diodes have remained limited to less than 10 \%, often measured below 100 mK temperature. In this work we take a new approach where non-reciprocity is induced by intrinsic SOC in a heavy metal Josephson barrier via the predicted supercurrent spin-Hall effect. By measuring a series of Nb-Pt-Nb nanopillar junctions we demonstrated field tuneable Josephson diode efficiencies as high as 17\%, measured above liquid Helium temperature. This was possible by the realization of a net non-equilibrium spin segregation in the Pt barrier, due to the supercurrent spin-Hall effect in the Pt barrier, analogous to the normal spin-Hall effect. As the direction of the induced spin moment is determined by the bias current, an external magnetic field causes the associated phases to add with opposite signs for opposite current directions, resulting in a nonreciprocal supercurrent across the junction.