Abstract
Emergent phenomena in transition-metal-oxide heterostructures such as interface superconductivity and magnetism have been attributed to electronic reconstruction, which, however, is difficult to detect and characterise. Here we overcome the associated difficulties to simultaneously address the electronic degrees of freedom and distinguish interface from bulk effects by implementing a novel approach to resonant X-ray reflectivity (RXR). Our RXR study of the chemical and valance profiles along the polar (001) direction of a LaCoO3 film on NdGaO3 reveals a pronounced valence-state reconstruction from Co3+ in the bulk to Co2+ at the surface, with an areal density close to 0.5 Co2+ ions per unit cell. An identical film capped with polar (001) LaAlO3 maintains the Co3+ valence over its entire thickness. We interpret this as evidence for electronic reconstruction in the uncapped film, involving the transfer of 0.5e− per unit cell to the subsurface CoO2 layer at its LaO-terminated polar surface.
| Original language | English |
|---|---|
| Article number | 16013 |
| Journal | npj Quantum Materials |
| Volume | 1 |
| DOIs | |
| State | Published - Sep 16 2016 |
Funding
We thank B Keimer and K Fürsich for helpful discussions. This work has been supported by the German Research Foundation DFG under grant number HA6470/1-2 and through SFB 1170 ‘ToCoTronics’ (project C04), as well as by the Canadian organisations NSERC, CFI and CRC. WSC was supported by the Basic Science Research Program through the National Research Foundation of Korea (NRF) funded by the Ministry of Science, ICT and future Planning (NRF-2014R1A2A2A01006478). Parts of the research were performed at the Max-Planck UBC Centre for Quantum Materials. Parts of the research were performed at the Canadian Light Source, which is funded by the Canada Foundation for Innovation, the Natural Sciences and Engineering Research Council of Canada, the National Research Council Canada, the Canadian Institutes of Health Research, the Government of Saskatchewan, Western Economic Diversification Canada and the University of Saskatchewan. The work at ORNL was supported by the U.S. Department of Energy, Office of Science, Basic Energy Sciences, Materials Sciences and Engineering Division.