Fig. 1: Electrical transport behavior of bulk RuO₂ single crystals and epitaxially strained RuO₂ thin films.

a, b Schematic diagrams of the crystal structures and in-plane lattice mismatches with TiO₂ substrates of RuO₂ thin films synthesized in (101)- and (110)-orientations. Gray and blue spheres represent Ru and O atoms, respectively. c Average resistivity versus temperature curves for 24.2 nm thick RuO₂(110) and 18.6 nm thick RuO₂(101) films, compared to results for bulk RuO₂ single crystals from Ref. ¹⁵. For clarity the bulk RuO₂ data have been rigidly shifted upward by 1 μΩ-cm (ρ₀  ≈  0.3  μΩ-cm). d V(I) curve measured at 0.6 K on a 10 μm-wide resistivity bridge lithographically patterned on the RuO₂(110) sample from (c) (as shown in the inset: scale bar  = 200  μm), which has the direction of current flow parallel to [001]_rutile. Similarly large critical current densities J_c are obtained with \(I| | [1\overline{1}0]\) (Supplementary Note 1 and Supplementary Fig. 1). e, f Upper critical magnetic fields H_c⊥ versus superconducting T_cs extracted from magnetoresistance measurements for the RuO₂(110) sample in (c) along with a characteristic R(H) sweep acquired at 0.45 K (inset in (f)). Superconducting T_cs are taken as the temperatures at which the resistance crosses 50% of its residual normal-state value R _4 K; error bars on these T_cs indicate where R crosses the 90% and 10% thresholds of R_4 K, respectively (cf. the horizontal dashed lines in (e)).