Triplet supercurrents in lateral Josephson junctions with a half-metallic ferromagnet

Physical Review Research, vol. 6

Abstract

In the area of superconducting spintronics, spin-triplet supercurrents in half-metallic ferromagnets (HMFs) could yield dissipationless spin transport over large distances and high current density. Promising among the HMFs is the perovskite oxide La 0.7 Sr 0.3 MnO 3 (LSMO), and recent studies in combination with the high- T c superconductor YBa 2 Cu 3 O 7 , or the conventional superconductor NbTi, showed long-range effects. Here we focus on two issues that as yet have received less attention: the value of the critical current in the HMF in the limit of a very small electrode distance (20 nm) and the nature of the spin-triplet generator. We use lateral junctions shaped as a bar, square, and disk, and find high supercurrent densities of the order of 10 11 A/ m 2 , pointing to an efficient triplet generation mechanism. This is surprising in the sense that no magnetic inhomogeneity is purposely built in, as is done in conventional metal triplet junctions. Furthermore, from the magnetic field dependence of the critical current interference patterns, we find a uniform supercurrent distribution in bar-shaped devices, but one more constricted to the rim in disk devices, which is an expected consequence of the geometry. We also analyze the temperature dependence of the critical current and find the quadratic dependence that was predicted in the limit of small junction lengths. From studying the NbTi/LSMO interface with scanning electron transmission microscopy, we conclude that the magnetic inhomogeneity required for triplet generation resides in the LSMO layer adjacent to the interface. Published by the American Physical Society 2024

Authors 5

1. Junxiang Yao Aachen Huygens-Kamerlingh Onnes Laboratory

   Leiden University

   Affiliation as printed

   Leiden University

   Huygens-Kamerlingh Onnes Laboratory, Leiden Institute of Physics, Leiden University, P.O. Box 9504, 2300 RA Leiden, The Netherlands

2. Remko Fermin

   University of Cambridge

   Affiliation as printed

   University of Cambridge

   Department of Materials Science & Metallurgy, University of Cambridge, 27 Charles Babbage Road, Cambridge CB3 0FS, United Kingdom

3. Mariona Cabero

   Universidad Complutense de Madrid

   Affiliation as printed

   Universidad Complutense de Madrid

4. Kaveh Lahabi Aachen Huygens-Kamerlingh Onnes Laboratory

   Leiden University

   Affiliation as printed

   Leiden University

   Huygens-Kamerlingh Onnes Laboratory, Leiden Institute of Physics, Leiden University, P.O. Box 9504, 2300 RA Leiden, The Netherlands

5. J. Aarts Aachen Huygens-Kamerlingh Onnes Laboratory

   Leiden University

   Affiliation as printed

   Leiden University

   Huygens-Kamerlingh Onnes Laboratory, Leiden Institute of Physics, Leiden University, P.O. Box 9504, 2300 RA Leiden, The Netherlands