Resonant X-ray spectroscopy studies on infinite-layer nickelates

The recent discovery of superconducting nickelates has drawn significant interest in the field. The nickelate superconductor is a Sr-doped infinite layer nickelate RNiO₂, which is isostructural to the infinite-layer cuprates and possesses the same nominal 3d electron count. Experimental investigations of the electronic structure and elementary excitations, such as magnetic excitations, can characterize the similarities and differences to the cuprates, providing important insight into the underlying microscopic mechanism in nickelate superconductors.

We use soft x-ray absorption spectroscopy (XAS) and resonant inelastic x-ray scattering (RIXS) to unravel the electronic structures of the infinite-layer nickelates. Unlike cuprates and other nickelates, we show that the parent compound of the infinite nickelates is in a different regime of the Zaanen-Sawatzky-Allen scheme. The rare earth space layer is not inert, but it supports a three-dimensional metallic state which hybridizes with a quasi-two-dimensional, strongly correlated state with 3d_x²-y² symmetry in the NiO₂ layers [1]. The strong correlation of the NiO₂ states is further supported by our observations of magnetic excitations [2] and a charge order [3], indicating the importance of Mott-physics in sculpting the electronic and magnetic structures of infinite layer nickelates. If time permits, I will also highlight some of our studies on other novel oxide systems.