Hybridization-controlled charge transfer and induced magnetism at correlated oxide interfaces

Abstract

At interfaces between conventional materials, band bending and alignment are classically controlled by differences in electrochemical potential. Applying this concept to oxides in which interfaces can be polar and cations may adopt a mixed valence has led to the discovery of novel two-dimensional states between simple band insulators such as LaAlO3 and SrTiO3. However, many oxides have a more complex electronic structure, with charge, orbital and/or spin orders arising from strong Coulomb interactions between transition metal and oxygen ions. Such electronic correlations offer a rich playground to engineer functional interfaces but their compatibility with the classical band alignment picture remains an open question. Here we show that beyond differences in electron affinities and polar effects, a key parameter determining charge transfer at correlated oxide interfaces is the energy required to alter the covalence of the metal-oxygen bond. Using the perovskite nickelate (RNiO3) family as a template, we probe charge reconstruction at interfaces with gadolinium titanate GdTiO3. X-ray absorption spectroscopy shows that the charge transfer is thwarted by hybridization effects tuned by the rare-earth (R) size. Charge transfer results in an induced ferromagnetic-like state in the nickelate, exemplifying the potential of correlated interfaces to design novel phases. Further, our work clarifies strategies to engineer two-dimensional systems through the control of both doping and covalence.

Metal-insulator-metal transition in NdNiO3 films capped by CoFe2O4

“…Nickel possesses one electron in e g orbit in Ni 3+ state, as illustrated in Fig. 4(d This is similar to the scenario reported in the previous publication, 8,[28][29][30] and a further low-temperature XMCD (x-ray magnetic circular dichroism) is expected to give an insight into the respective contribution to magnetism during the transition. But this is not the case for the 3 u.c.…”

Reproducibility and off-stoichiometry issues in nickelate thin films grown by pulsed laser deposition

“…This result is consistent with our observation of a preserved covalency after electron transfer into a nickelate from a rare-earth titanate film. 31 Additionally, from the energy separation between the Ni-2p 3/2 main line and feature III (i.e. ∆E sat as indicated in Figure 4b), we can obtain further important information related to the transport properties of the NNO series.…”

Charge Transfer in Iridate-Manganite Superlattices

“…We also construct a phenomenological model to understand the microscopic mechanism of the surprising charge transfer at SIO/SMO interfaces. This phenomenological model is based on molecular orbitals formed at the interface and naturally predicts unique strain dependence of the charge transfer, which we confirm by DFT calculations and verify experimentally.The charge transfer across non-polar interfaces was also discussed between GdTiO 3 and perovskite nickelates [22]. The amount of charge redistribution is controlled by the covalent character of the transition metal/oxygen bonds.…”