Figure 1: Structure of Au/SrRuO₃/Sr₂RuO₄ devices.

(a) A schematic depiction of a spin-singlet superconductor (SSC) based ferromagnetic-metal (FM)/FM′/SSC junction, where a special kind of complex magnetic inhomogeneity (the FM′ layer) is always required. (b) For spin-triplet superconductor (TSC) based FM/TSC junctions, spin-polarized supercurrent directly penetrates into FM without any magnetic inhomogeneity, and importantly, with undisturbed spin information. (c) Transmission electron microscope image of the interfacial region of a 15-nm-thick SrRuO₃ thin film deposited on the cleaved ab surface of Sr₂RuO₄ substrate taken along its [010] direction. The scale bar at the left bottom corresponds to 1nm. The region indicated by the white rectangle is shown at a higher magnification on the right-hand side, together with a schematic illustration of the Ru (purple) and Sr (green) atomic positions. (d) Three-dimensional (3D) schematic image of a Au(600-nm)/SrRuO₃(15-nm)/Sr₂RuO₄ junction. SrRuO₃ square pads of the area 25 × 25 μm² and 10 × 10 μm² are formed by etching to fabricate the 20 × 20 μm² (Junction A) and 5 × 5 μm² (Junction B) junctions. A 300-nm thick SiO₂ layer is deposited to electrically isolate the top Au electrode from the Sr₂RuO₄ substrate. As shown in the inset, during the fabrication process, the Sr₂RuO₄ substrate surface was etched by ≈30 nm except for the area under the Sr₂RuO₃ pads, resulting in ‘necks’ of Sr₂RuO₄. (e) Optical microscope image of a device containing six different junctions. The brighter regions are the top Au electrodes. The scale bar at the right bottom corresponds to 200 μm. Inset shows a magnified image taken within the black rectangular area in which a 5 × 5 μm² junction (step in the center of Au pad) is located. The purple square indicates the SrRuO₃ pad (10 × 10 μm²) under the top Au electrode. The scale bar is equivalent to 20 μm.