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.