Complex oxides exhibit a rich array of properties as a result of the degrees of freedom that can be achieved by the choice of metal cations. This richness has been built upon by preparing interfaces of dissimilar perovskites. One of the most interesting and widely investigated systems of this kind is the LaAlO3/SrTiO3(001) (LAO/STO) heterojunction. Despite the fact that both materials are band insulators, their interface can exhibit electronic conductivity. These results have been widely interpreted as being due to an electronic reconstruction (or charge transfer) resulting from the polarity mismatch between LAO and STO, giving rise to a two-dimensional electron gas on the STO side of the interface. However, it is also known that this interface exhibits significant cation mixing, and certain intermixed configurations have been shown theoretically to eliminate the interface dipole, in addition to inducing conductivity by unintentional La doping of the underlying STO.
Inasmuch as the LAO/STO interface has been very heavily studied, it is of interest to explore other related materials systems. To this end, we have investigated the LaCrO3/SrTiO3(001) (LCO/STO) heterojunction, as prepared by molecular beam epitaxy. Core-level and valence-band x-ray photoemission spectra yield band offsets and potential gradients within the LaCrO3 sufficient to trigger an electronic reconstruction to alleviate the polarity mismatch. Yet, the interface is insulating. Based on first principles calculations, we attribute this unexpected result to interfacial cation mixing combined with charge redistribution within CrO2 layers, enabled by low-lying d states within LaCrO3, which suppresses.