Ferromagnetic Materials for Josephson π Junctions

Abstract

The past two decades have seen an explosion of work on Josephson junctions containing ferromagnetic materials. Such junctions are under consideration for applications in digital superconducting logic and memory. In the presence of the exchange field, spin-singlet Cooper pairs from conventional superconductors undergo rapid oscillations in phase as they propagate through a ferromagnetic material. As a result, the ground-state phase difference across a ferromagnetic Josephson junction oscillates between 0 and $\pi$ as a function of the thickness of the ferromagnetic material. $\pi$-junctions have been proposed as circuit elements in superconducting digital logic and in certain qubit designs for quantum computing. If a junction contains two or more ferromagnetic layers whose relative magnetization directions can be controlled by a small applied magnetic field, then the junction can serve as the foundation for a memory cell. Success in all of those applications requires careful choices of ferromagnetic materials. Often, materials that optimize magnetic properties do not optimize supercurrent propagation, and vice versa. In this review we discuss the significant progress that has been made in identifying and testing a wide range of ferromagnetic materials in Josephson junctions over the past two decades. The review concentrates on ferromagnetic metals, partly because eventual industrial applications of ferromagnetic Josephson junctions will most likely start with metallic ferromagnets (either in all metal junctions or junctions containing also an insulating layer). We will briefly mention work on non-metallic barriers, including ferromagnetic insulators, and some of the exciting work on spin-triplet supercurrent in junctions containing noncollinear magnetic inhomogeneity.

Revised version with many additional references. 69 pages, 2 figures

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Cited by in corpus (21)

• Josephson diode effect with Andreev and Majorana bound states
• Quantum-geometric spin and charge Josephson diode effects
• Theory of quantum-geometric charge and spin Josephson diode effects in strongly spin-polarized hybrid structures with noncoplanar spin textures
• The physics of superconductor-ferromagnet hybrid structures
• Buzdin, Shapiro and Chimera Steps in ${\phi }_0$ Josephson Junctions. II. Bifurcation, Switching, and Hysteresis
• Upper critical fields in normal metal-superconductor-normal metal trilayers
• Bending-strain effects in conventional superconductors and superconducting junctions
• Reduced decay in Josephson coupling across ferromagnetic junctions with spin-orbit coupling layers
• Spin-split superconductivity in spin-orbit coupled hybrid nanowires with ferromagnetic barriers
• Effect of 2${}^{\text{nd}}$ harmonic current--phase relation on a behavior of a Josephson Traveling Wave Parametric Amplifier
• Proposal for spin superfluid quantum interference device
• Evidence of the inverse proximity effect in tunnel magnetic Josephson Junctions
• Superluminal Propagation of Composite Collective Modes in Superconductor-Ferromagnet Heterostructures
• Low-loss Nb on Si superconducting resonators from a dual-use spintronics deposition chamber and with acid-free post-processing
• Comparison of NiFeCr and NiFe in ferromagnetic Josephson junctions
• Josephson diode and spin-valve effects on the surface of altermagnet CrSb
• Percolative supercurrent in superconductor-ferromagnetic insulator bilayers
• Intrinsic space-time crystalline order in a hybrid Josephson junction
• Demonstration of 0-pi transition in Josephson junctions containing unbalanced synthetic antiferromagnets
• Large critical current density Josephson $\pi$ junctions with PdNi barriers
• Submicrometer tunnel ferromagnetic Josephson junctions with transmon energy scale