Weak antilocalization and sign inversion of magnetoresistance on CaRuO₃ epitaxial films

CaRuO₃ is a prototypical perovskite oxide among the Ruddlesden-Popper series with multi-exotic physical properties on the verge of quantum criticality. Unlike the case of the well-known ferromagnetic SrRuO₃, the literature on the physical properties of the CaRuO₃ system is scarce with no consensus about its magnetic and transport ground states. This work provides a detailed study of the magnetotransport properties of 300 nm CaRuO₃ epitaxial films grown on single crystalline SrTiO₃ and LaAlO₃ substrates. The magnetic and electronic ground states in tensile strained CaRuO₃/SrTiO₃ films and compressively strained CaRuO₃/LaAlO₃ films are found to be distinctly different. In particular, in zero magnetic field, the high-temperature resistivity of both films show a T 1 / 2 non-Fermi liquid behavior. Cooling below 30 K, CaRuO₃/SrTiO₃ undergoes metal-insulator-transition ascribed by 3D weak localization, with signs of weak ferromagnetic-like domains. By contrast, the transport data of the nonmagnetic CaRuO₃/LaAlO₃ film below 30 K, show T^3/2 non-Fermi liquid type behavior. Magnetoresistance in CaRuO₃/SrTiO₃ shows combination of weak antilocalization and weak localization behaviors deep in the insulating side, emphasizing the existence of spin-orbit coupling and the strong influence of ferromagnetic impurities. Moreover, the nonlinearity signals in CaRuO₃/SrTiO₃ Hall measurements could be described by anomalous Hall effects. Interestingly, below 30 K, magnetoresistance and Hall in CaRuO₃/LaAlO₃ change sign, indicating an inversion from hole-like to electron-like behavior. We discuss the sensitivity of the 300 nm CaRuO₃/SrTiO₃ and CaRuO₃/LaAlO₃ films to the 30 K temperature, an additional quantum critical feature to the ruthenate oxides.