Jacobo Santamaría

The Josephson effect results from the coupling of two superconductors across a non-superconducting spacer to yield a quantum coherent state. In ferromagnets, singlet (opposite-spin) Cooper pairs decay over very short distances, and thus Josephson coupling requires a nanometric spacer. This is unless equal-spin triplet pairs are generated which, theoretically, can couple superconductors across much longer distances. Despite many experimental hints of triplet superconductivity at ferromagnet/superconductor interfaces, long range triplet Josephson effects across ferromagnetic barriers have remained elusive. In this talk I will discuss a micron-range Josephson coupling in planar junctions across the half-metallic ferromagnet La_0.7Sr_0.3MnO₃ combined with the high-temperature superconductor YBa₂Cu₃O₇. These display the hallmarksof the Josephson physic, namely critical current oscillations due to flux quantization (Fraunhofer pattern) and phase locking under microwave excitation (Shapiro steps) [1]. The marriage of high-temperature quantum coherent transport and full spin polarization brings unique opportunities for the practical realization of superconducting spintronics, and enables novel strategies for devices in quantum technologies.

[1] Nature Mater (2021), in print

Work done in collaboration with D. Sanchez-Manzano¹, S. Mesoraca², F. Cuellar¹, M. Cabero³, V. Rouco¹, G. Orfila¹, X. Palermo², A. Balan², L. Marcano⁵, A. Sander², M. Rocci¹, J. Garcia-Barriocanal ⁵, F. Gallego¹, J. Tornos¹, A. Rivera¹, F. Mompean^6., M. Garcia-Hernandez ⁶, J. M. Gonzalez-Calbet³, C. Leon¹, S. Valencia⁵, C. Feuillet-Palma⁷, N. Bergeal⁷, A.I. Buzdin⁸, J. Lesueur⁷, Javier E. Villegas², J. Santamaria^1,*.

1 GFMC. Dept. Fisica de Materiales. Facultad de Fisica. Universidad Complutense. 28040 Madrid

2 Unité Mixte de Physique, CNRS, Thales, Université Paris-Saclay, 91767 Palaiseau. France

3 Centro Nacional de Microscopia Electronica. Universidad Complutense 28040 Madrid.

4 Helmholtz-Zentrum Berlin für Materialien und Energie, Albert-Einstein-Strasse 15, D-12489, Berlin, Germany

5 Characterization Facility, University of Minnesota, 100 Union St, Minneapolis, MN 55455, USA

6 Instituto de Ciencia de Materiales de Madrid ICMM-CSIC 28049 Cantoblanco. Spain

7 Laboratoire de Physique et d’Etude des Matériaux, CNRS, ESPCI Paris, PSL Research University, UPMC, 75005, Paris, France

8 Université Bordeaux, CNRS, LOMA, UMR 5798, F-33405 Talence, France