Dimensionality-Controlled Evolution of Charge-Transfer Energy in Digital Nickelates Superlattices.

Fundamental understanding and control of the electronic structure evolution in rare-earth nickelates is a fascinating and meaningful issue, as well as being helpful to understand the mechanism of recently discovered superconductivity. Here the dimensionality effect on the ground electronic state in high-quality (NdNiO ₃ ) _m /(SrTiO ₃ ) ₁ superlattices is systematically studied through transport and soft X-ray absorption spectroscopy. The metal-to-insulator transition temperature decreases with the thickness of the NdNiO ₃ slab decreasing from bulk to 7 unit cells, then increases gradually as m further reduces to 1 unit cell. Spectral evidence demonstrates that the stabilization of insulating phase can be attributed to the increase of the charge-transfer energy between O 2p and Ni 3d bands. The prominent multiplet feature on the Ni L ₃ edge develops with the decrease of NdNiO ₃ slab thickness, suggesting the strengthening of the charge disproportionate state under the dimensional confinement. This work provides convincing evidence that dimensionality is an effective knob to modulate the charge-transfer energy and thus the collective ground state in nickelates.
(© 2022 The Authors. Advanced Science published by Wiley-VCH GmbH.)