Infinite-layer/perovskite oxide heterostructure-induced high-spin states in SrCuO₂/SrRuO₃bilayer films

Heterostructures composed of dissimilar oxides with different properties offer opportunities to develop emergent devices with desired functionalities. A key feature of oxide heterostructures is interface electronics and orbital reconstructions. Here, we combined infinite-layered SrCuO2 and perovskite SrRuO3 into heterostructures. A rare high spin state as large as 3.0 μB f.u-1 and an increase in Curie temperature by 12 K are achieved in an ultrathin SrRuO3 film capped by a SrCuO2 layer. Atomic-scale lattice imaging shows the uniform CuO2-plane-to-RuO5-pyramid connection at the interface, where the regularly arranged RuO5 pyramids were elongated along the out-of-plane direction. As revealed by theoretical calculations and spectral analysis, these features finally result in an abnormally high spin state of the interfacial Ru ions with highly polarized eg orbitals. The present work demonstrates that oxygen coordination engineering at the infinite-layer/perovskite oxide interface is a promising approach towards advanced oxide electronics.