Giant orbital polarization of Ni 2+ in a square planar environment

Abstract

Finding large orbital polarization in Ni-based oxides has become a topic of paramount interest in recent years due to the prospect of finding superconductivity. In this work, we investigate the electronic structure of single-crystalline samples of Sr2CuO3 and Ni-doped Sr 2 CuO3 containing Cu/NiO4 square planar units. Our polarization-dependent x-ray absorption spectroscopy experiments reveal extremely large orbital polarization (∼63%)for Ni2+. Cluster calculations and ab initio calculations find that the giant orbital polarization arises due to the low-spin (S=0) configuration with two holes in the Ni 3dx2−y2 orbital, contrary to the expected high-spin ( S=1) state from Hund's first rule.