Metal-insulator transition in (111) SrRuO₃ ultrathin films

(111)-oriented transition metal oxide thin films provide a route to developing oxide-based topological quantum materials, but the epitaxial growth is challenging. Here, we present the thickness-dependent electronic and magnetic phase diagrams of coherently strained, phase pure (111)-oriented SrRuO3 epitaxial films grown on (111) SrTiO3 substrates using pulsed laser deposition. With decreasing film thickness, it is found that both the metal-to-insulator and magnetic phase transitions occur at the same thickness of 4–5 nm for films grown along both the (111) and the (001) directions. The character of the transport near the metal-insulator transition is, however, distinct for the different directions, which is attributed to the increased electron-electron correlation for (111) SrRuO3. The findings presented here highlight both the broad challenges as well as the possibilities in modifying correlated materials using dimensional tuning of electronic and magnetic properties.