Dimensionality-controlled evolution of charge-transfer energy in digital nickelates superlattices

TL;DR

This study explores how reducing the dimensionality in nickelate superlattices affects their electronic structure, particularly the charge-transfer energy, which influences their metal-insulator transition and charge disproportionation.

Contribution

It provides systematic experimental evidence that dimensionality controls charge-transfer energy and ground state properties in nickelate superlattices, advancing understanding of their electronic phase behavior.

Findings

Decreased NdNiO3 thickness lowers the metal-insulator transition temperature.

Charge-transfer energy increases with reduced dimensionality, stabilizing the insulating phase.

Charge disproportionation becomes more pronounced as the superlattice thickness decreases.

Abstract

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 we systematically study the dimensionality effect on the ground electronic state in high-quality (NdNiO3)m/(SrTiO3)1 superlattices through transport and soft x-ray absorption spectroscopy. The metal-to-insulator transition temperature decreases with the thickness of the NdNiO3 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 L3 edge develops with the decrease of NdNiO3 slab thickness, suggesting the strengthening of the charge disproportionate state under the dimensional confinement. Our work provides convincing evidence that dimensionality is an effective knob to modulate the charge-transfer energy and thus the collective ground state in nickelates.