The atomic-scale structure and the bonding topology in a material determines its resulting properties. Alterable or reversible bond distortions at the picometer length scale in turn modify a material's electronic configuration and can give rise to functional properties. Picoscale bond perturbations represent the ultimate length scale for materials engineering:* any smaller and the effects are too small to matter; any larger and the bonds are completely broken so we are describing a different material. I will describe, using first principles theory together with parallel experimental results from my Yale collaborators, two examples where we can understand and/or design picoscale distortions in 3d transition metal oxides in order to control electron transport or relative orbital energies and occupancies. The first system is an oxide/oxide ferroelectric mobility-effect device (not field effect), while the second material is an artificially designed oxide superlattice that achieves strong orbital polarization and strong antiferromagnetic inter-layer coupling. * Ismail-Beigi, Walker, Disa, Rabe, and Ahn, “Picoscale materials engineering,” Nature Reviews Materials 2, 17060 (2017).
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