Controllable 0-pi Josephson junctions containing a ferromagnetic spin valve

TL;DR

This paper demonstrates experimentally controllable 0-pi Josephson junctions using ferromagnetic layers, enabling toggling of phase states for potential applications in cryogenic memory and superconducting logic circuits.

Contribution

It introduces a method to control the phase state of Josephson junctions with ferromagnetic layers by changing magnetization orientations, advancing superconducting circuit technology.

Findings

Phase state can be toggled between 0 and pi by magnetic orientation.

Controllable junctions enable applications in cryogenic memory.

Potential for superconducting programmable logic circuits.

Abstract

Superconductivity and ferromagnetism are antagonistic forms of order, and rarely coexist. Many interesting new phenomena occur, however, in hybrid superconducting/ferromagnetic systems. For example, a Josephson junction containing a ferromagnetic material can exhibit an intrinsic phase shift of pi in its ground state for certain thicknesses of the material. Such "pi-junctions" were first realized experimentally in 2001, and have been proposed as circuit elements for both high-speed classical superconducting computing and for quantum computing. Here we demonstrate experimentally that the phase state of a Josephson junction containing two ferromagnetic layers can be toggled between 0 and pi by changing the relative orientation of the two magnetizations. These controllable 0-pi junctions have immediate applications in cryogenic memory where they serve as a necessary component to an ultra-low power superconducting computer. Such a fully superconducting computer is estimated to be orders of magnitude more energy-efficient than current semiconductor-based supercomputers. Phase controllable junctions also open up new possibilities for superconducting circuit elements such as superconducting "programmable logic," where they could function in superconducting analogs to field-programmable gate arrays.