Modulation of metal-insulator transitions of NdNiO/LaNiO/NdNiO trilayers via thickness control of the LaNiO layer.

Over the last few decades, manipulating the metal-insulator (MI) transition in perovskite oxides (ABO) via an external control parameter has been attempted for practical purposes, but with limited success. The substitution of A-site cations is the most widely used technique to tune the MI transition. However, this method introduces unintended disorder, blurring the intrinsic properties. The present study reports the modulation of MI transitions in [10 nm-NdNiO/t-LaNiO/10 nm-NdNiO/SrTiO (100)] trilayers (t = 5, 7, 10, and 20 nm) via the control of the LaNiO thickness. Upon an increase in the thickness of the LaNiO layer, the MI transition temperature undergoes a systematic decrease, demonstrating that bond disproportionation, the MI, and antiferromagnetic transitions are modulated by the LaNiO thickness. Because the bandwidth and the MI transition are determined by the Ni-O-Ni bond angle, this unexpected behavior suggests the transfer of the bond angle from the lower layer into the upper. The bond-angle transfer eventually induces a structural change of the orthorhombic structure of the middle LaNiO layer to match the structure of the bottom and the top NdNiO, as evidenced by transmission electron microscopy. This engineering layer sequence opens a novel pathway to the manipulation of the key properties of oxide nickelates, such as the bond disproportionation, the MI transition, and unconventional antiferromagnetism with no impact of disorder.