Room-Temperature Possible Current-Induced Transition in CaRuO Thin Films Grown Through Intercalation-Like Cation Diffusion in the ABO Ruddlesden-Popper Structure.

Cation deficiency tuning is a central issue in thin-film epitaxy of functional metal oxides, as it is typically more difficult than anion deficiency tuning, as anions can be readily supplied from gas sources. Here, highly effective internal deficiency compensation of Ru cations is demonstrated for CaRuO epitaxial films based on diffusive transfer of metal cations in the ABO Ruddlesden-Popper lattice from solid-phase cation sources. Through detailed structural characterization of CaRuO/LaAlO (001) thin films grown with external cation sources by solid-phase epitaxy, the occurrence of intercalation-like, interstitial diffusion of La cations (from the substrates) in the ABO structure is revealed, and that of Ru cations is also suggested. Relying on the interstitial-type diffusion, an optimized Ru deficiency compensation method, which does not induce the formation of Ca RuO Ruddlesden-Popper impurity phases with higher n, is proposed for CaRuO epitaxial films. In the CaRuO/LaAlO (001) thin films grown with Ru deficiency compensation, record-high resistivity values (10-10 Ω cm) and a large (more than 200 K) increase in the temperature range of the nonlinear transport properties are demonstrated by transport measurements, demonstrating the possible advantages of this method in the control of the current-induced quantum phase transition of CaRuO.