Superconducting coupling between two regions separated by a one micron wide ferromagnetic compound has been proved by an international team. This macroscopic quantum effect, known as Josephson effect, generates an electrical current within the ferromagnetic compound made of superconducting Cooper-pairs. Magnetic imaging of the ferromagnetic region at BESSY II has contributed to demonstrate that the spin of the electrons forming the Cooper pairs are equal. These results pave the way for low-power consumption superconducting spintronic-applications where spin-polarized currents can be protected by quantum coherence.
When two superconducting regions are separated by a strip of non-superconducting material, a special quantum effect can occur, coupling both regions: The Josephson effect. If the spacer material is a half-metal ferromagnet novel implications for spintronic applications arise. An international team has now for the first time designed a material system that exhibits an unusually long-range Josephson effect: Here, regions of superconducting YBa2Cu3O7 are separated by a region of half-metallic, ferromagnetic manganite (La2/3Sr1/3MnO3) one micron wide.
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Image: Device where the long range Josephson coupling has been demonstrated. Superconducting YBa2Cu3O7 regions (yellow) are separated by a half-metal La2/3Sr1/3MnO3 ferromagnet (green).
Credit: © Nature Materials 2021: 10.1038/s41563-021-01162-5