Visualizing short-range charge transfer at the interfaces between ferromagnetic and superconducting oxides

The interplay between antagonistic superconductivity and ferromagnetism has been a interesting playground to explore the interaction between competing ground states. Although this effect in systems of conventional superconductors is better understood, the framework of the proximity effect at complex-oxide-based superconductor/ferromagnet interfaces is not so clear. The main difficulty originates from the lack of experimental tools capable of probing the interfaces directly with high spatial resolution. Here we harness cross-sectional scanning tunnelling microscopy and spectroscopy together with atomic-resolution electron microscopy to understand the buried interfaces between cuprate and manganite layers. The results show that the fundamental length scale of the electronic evolution between YBa 2 Cu 3 O 7− δ (YBCO) and La 2/3 Ca 1/3 MnO 3 (LCMO) is confined to the subnanometre range. Our findings provide a complete and direct microscopic picture of the electronic transition across the YBCO/LCMO interfaces, which is an important step towards understanding the competition between ferromagnetism and superconductivity in complex-oxide heterostructures. Interesting proximity effects can occur at the interface of superconducting and ferromagnetic oxides, but they are poorly understood. Here, the authors use scanning tunnelling and electron microscopy techniques to investigate such an interface, showing that the charge transfer has an upper limit of 1 nm.