Low spin configuration and giant orbital polarization of Ni<sup>2+</sup> in square planar environment
ORAL
Abstract
The high Tc superconductivity in nickelates has been finally discovered in Sr0.2Nd0.8NiO2, in which Ni is in square planar (D4h) coordination of oxygen. Despite being iso-electronic (3d9), the parent compounds of nickelate and cuprate superconductors have markedly different electronic and magnetic behavior. To understand this, we have investigated the electronic and magnetic structure of Sr2CuO3 and Sr2Cu0.9Ni0.1O3. These compounds provide a unique opportunity to compare the electronic structure of both Ni and Cu in square planar (D4h) environment. Polarization-dependent X-ray absorption spectroscopy (XAS) at Ni L3,2 edge revealed extremely large (∼ 63%) orbital polarization (OP) for Ni. Our simulations based on multiplet ligand field theory for polarization dependent XAS of Ni2+ and the results from ab initio density functional theory have revealed that such high orbital polarization arises due to two holes in Ni 3dx2-y2 that give rise to nonmagnetic S = 0 state of Ni2+ - in contrast to S = 1 state from Hund’s first rule. Such nonmagnetic S = 0 Ni2+ in hole dope nickelate would be analogous to the Zhang Rice singlet.
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Presenters
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Prithwijit Mandal
- Indian Institute of Science Bangalore