Emergent electronic and magnetic properties of spatially confined ruthenates

Heterostructures of complex transition metal oxides are known to induce extraordinary quantum states that arise from broken symmetry and other discontinuities at interfaces. One of the currently existing issues is to reveal the origin of these emergent states. In this talk, I will focus on some unusual behaviors of the interfaces and thin films/heterostructures of ruthenates. Emergence of unusual, thickness-dependent ferromagnetic and transport properties in ultrathin CaRuO3 films is found through a unique insertion of a single isovalent SrO layer (referred to as "?-doping"). While bulk CaRuO3 is metallic and nonmagnetic, films thinner than or equal to ~15-unit cells (u.c.) are insulating though still nonmagnetic. However, ?-doping to middle of such CaRuO3 films induces an insulator-to-metal transition and ferromagnetism with unusual magnetoresistive behavior. The results highlight the delicate nature of magnetic instability in CaRuO3 and subtle effects that can alter it, especially the role of A-site cation in electronic and magnetic structure additional to lattice distortion. On the other hand, the insertion of SrRuO3 monolayer into SrTiO3 films results in nonmagnetic and insulating character. the results indicate that the observed non-stoichiometry is the cause of the observed loss of metallicity and ferromagnetism in the monolayer SrRuO3.