Van der Waals ferromagnet exhibits long-distance skin Josephson supercurrent, team discovers.

In a study published in Nature Communications, the group of Professor Xiang Bin of the University of Science and Technology of China of the Chinese Academy of Sciences, in collaboration with Assoc. Professor Wang Zhi of Sun Yat-sen University discovered the long-range Josephson supercurrent through van der Waals magnets.

They connected two NbSe superconductors₂ (S) By creating van der Waals iron metal and ferromagnets₃ GeTe₂(F), and observed a long-range supercurrent in a lateral Josephson junction (S/F/S) for the first time, which shows striking skin properties.

Ferromagnetism and superconductivity are two opposite macroscopic orders. When the singlet supercurrent enters the ferromagnet, the rapid decoherence of the Cooper pairs will be triggered.

However, spin-triplet supercurrents induced near superconductor/ferromagnet interfaces enable transport without energy dissipation over long distances in ferromagnets, which has been demonstrated both theoretically and experimentally in recent years. This provides a more desirable way to build quantum devices without dissipation.

Previous research focused on constructing superconducting Josephson junctions with conjugated bulk ferromagnets to achieve monitoring of triple spin currents and control of spin and charge degrees of freedom. However, there are few reports on the observation of spin-triplet supercurrents and related studies of interfacial properties based on heterojunctions of two-dimensional (2D) van der Waals (vdW) materials.

Researchers constructed vdW Josephson side junctions of S/F/S by bridging two single VdW NbSe superconductors.₂ With vdW ferromagnet Fe₃GeTe₂ (F). The electrical properties of S/F/S with different junction channel lengths have been studied by low-temperature electrical tests. The results show a zero resistance case of S/F/S and ultra-long range (~300 nm) Josephson current.

The zero-temperature superconducting critical current tends to decay with increasing channel length and completely disappears when channel length increases to 450 nm.

Most interestingly, the response of the long-range superconducting critical current to an external magnetic field perpendicular to the supercurrent channel presented a periodic oscillation pattern, resembling a two-slit interferogram, instead of the conventional Fraunhofer periodic oscillation band. This result confirmed the existence of a superconducting Josephson current with a long-range skin feature in the S/F/S that is distinct from the superconducting Josephson current of conventional bulk channels.

In addition, the researchers proposed two possible mechanisms for the skin feature of the long-range supercurrent. First, the Rashba rotational coupling induced by mirror symmetry breaking on iron₃GeTe₂surface, upon interaction with the ferromagnetism and s-wave superconductivity of NbSe₂ may lead to two-dimensional topological superconductivity on iron₃GeTe₂ Surface.

Secondly, the magnetic inhomogeneities caused by the uneven structure of the iron atoms in Fe₃GeTe₂It promotes the conversion of single spin Cooper pairs into triple spin pairs on the surface through spin spin and spin mixing, and then forms a long range Josephson supercurrent.

The S/F/S design of the non-planar structure provides a new perspective to explore the interaction between ferromagnetism and superconductivity. The new physical properties presented by this non-planar structure provide a platform for potential applications of novel quantum functional devices in 2D superconducting spin electronics and the realization of topological superconductivity.