Orbital and spin character of doped carriers in infinite-layer nickelates

The recent discovery of superconductivity in Nd1-xSrxNiO2 has drawn significant attention in the field. A key open question regards the evolution of the electronic structure with respect to hole doping. Here we exploit x-ray absorption spectroscopy (XAS) and resonant inelastic x-ray scattering (RIXS) to probe the doping-dependent electronic structure of Nd1-xSrxNiO2. Upon doping, a high-energy feature in Ni L-3-edge XAS develops in addition to the main absorption peak, while XAS at the O K-, Nd M-3- and Nd M-5-edge exhibits a much weaker response. This implies that doped holes are mainly introduced into Ni 3d states. By comparing our data to atomic multiplet calculations including D-4h crystal field, the doping-induced feature in Ni L-3-edge XAS is consistent with a d(8) spin-singlet state in which doped holes reside in the 3d(x2-y2) orbitals. This is further supported by the softening of RIXS orbital excitations due to doping, corroborating with the Fermi level shift associated with increasing holes in the Ni 3d(x2-y2) orbital.

Automated summary

The discovery of superconductivity in Nd1-xSrxNiO2 has sparked interest in the field, particularly regarding how the electronic structure evolves with hole doping. Using x-ray absorption spectroscopy and resonant inelastic x-ray scattering, researchers investigated the doping-dependent electronic structure and found that doped holes are mainly introduced into Ni 3d states. Comparing the data to atomic multiplet calculations, they concluded that the features observed in the XAS are consistent with a d(8) spin-singlet state in the 3d(x2-y2) orbitals.