Capping effects on spin and charge excitations in parent and superconducting Nd1-xSrxNiO2

TL;DR

This study uses RIXS to analyze how SrTiO3 capping layers affect spin and charge excitations in Nd1-xSrxNiO2, revealing intrinsic magnetism and minimal capping-induced changes in these nickelates.

Contribution

It provides the first detailed investigation of capping effects on Nd1-xSrxNiO2's excitations, highlighting the intrinsic nature of magnetism and minimal impact of capping layers.

Findings

Spin excitations are present regardless of capping, indicating intrinsic magnetism.

Capping slightly increases the energy of spin excitations.

Reduced Ni-Nd charge transfer peak suggests decreased hybridization in capped samples.

Abstract

Superconductivity in infinite layer nickelates Nd1-xSrxNiO2 has so far been achieved only in thin films raising questions on the role of substrates and interfaces. Given the challenges associated with their synthesis it is imperative to identify their intrinsic properties. We use Resonant Inelastic X-ray Scattering (RIXS) to investigate the influence of the SrTiO3 capping layer on the excitations of Nd1-xSrxNiO2 (x = 0 and 0.2). Spin excitations are observed in parent and 20% doped Nd1-xSrxNiO2 regardless of capping, proving that magnetism is intrinsic to infinite-layer nickelates and appears in a significant fraction of their phase diagram. In parent and superconducting Nd1-xSrxNiO2, the spin excitations are slightly hardened in capped samples compared to the non-capped ones. Additionally, a weaker Ni - Nd charge transfer peak at ~ 0.6 eV suggests that the hybridization between Ni 3d and Nd 5d orbitals is reduced in capped samples. From our data, capping induces only minimal differences in Nd1-xSrxNiO2 and we phenomenologically discuss these differences based on the reconstruction of the SrTiO3 - NdNiO2 interface and other mechanisms such as crystalline disorder.