Nanoscale Domain Wall Engineered Spin-Triplet Josephson Junctions and SQUID

Abstract

Spin-singlet Cooper pairs convert to spin-triplet Cooper pairs on passing through a magnetically noncollinear structure at a superconductor(S)/ ferromagnet(F) interface. In this context, the generation of triplet supercurrents through intrinsic ferromagnetic domain walls, which are naturally occurring noncollinear magnetic features, was proposed theoretically in the past decade. However, an experimental demonstration has been lacking in the literature, particularly because of the difficulty in accessing a single domain wall, which is typically buried between two domains in a ferromagnetic material. By patterning a ferromagnetic nanoconstriction, we have been able to realize a nanoscale S/F/S planar junction, where a single domain wall (pinned at the nanoconstriction) acts as a Josephson barrier. In this geometry, we are able to show the predicted longrange triplet supercurrent across a ferromagnetic barrier exceeding 70 nm. Using this technique, we have demonstrated a ferromagnetic planar nano-SQUID device consisting of two Nb/Ni/Nb spin-triplet Josephson junctions.

Josephson spin-valve realization in the magnetic nodal-line topological semimetal Fe$_3$GeTe$_2$

“…Regarding the effects of the domain structure, one should note that the presence of several ferromagnetic domains between the superconducting leads could generally give rise to essentially the same physics as in a JSV 63,64 . In particular, asymmetric non-Fraunhofer I c (B) patterns in SFS junctions with a complex multi-domain structure have been reported before 54,55 .…”

Superconducting Triplet Rim Currents in a Spin-Textured Ferromagnetic Disk

“… 29 , 30 However, the experimental evidence to verify such models remains scarce. 31 In other recent developments, it was suggested that theoretically spin mixing can also be achieved by spin–orbit coupling (SOC). 32 − 36 This led to researching long-range proximity effects with Josephson junctions containing heavy metal interlayers.…”

Controllable two- and three-state magnetization switching in single-layer epitaxial Pd1−xFex films and an epitaxial Pd0.92Fe0.08/Ag/Pd0.96Fe0.04 heterostructure

“…The generation of the long-range triplet component of the superconducting pairing at noncollinear orientations of magnetization in ferromagnetic layered systems is extensively studied in the framework of magnetic Josephson junctions (MJJs) ([ 1 – 3 ] for early works, and [ 4 – 5 ] for very recent papers), and superconductive spin valves (SSVs) [ 6 – 9 ]. The key points of the underlying physics are non-uniform magnetic configurations in the system that mix singlet and triplet superconducting pairing channels.…”