Metal-insulator transition in ultrathin rutile RuO₂ films

Emergence of superconductivity in anisotropically strained rutile RuO₂ thin films has shown strain as an effective control knob to induce electronic phases that are absent in the bulk. By controlling film thickness, and thereby epitaxial strain and dimensionality, we reveal a metallic to insulating transition in RuO₂/TiO₂ (110) films with decreasing thicknesses. Atomically-smooth, epitaxial films were grown using solid-source metal-organic molecular beam epitaxy approach. Hall bar devices with current channels along two in-plane directions [001] and [10] revealed anisotropic transport. Quantitative analysis of the temperature-dependent magnetotransport data revealed, the transition from metallic to insulating state is driven via strong electron-electron interactions. By combining transport and spectroscopy measurements, we discuss the interplay between dimensionality, and electron correlation and their influence on the origin of metal-to-insulator transition in RuO₂ films.