Séminaires IQ/RQMP: Yao Shen
Date : 14 November 2022 11:00
Type : Institut Quantique
Location : Atrium D9 et Zoom
Cookies will be available in the IQ kitchenette starting at 10:30, at which time coffee will be free until 11:00. Talk starts at 11:00. A nice occasion to discuss
Title: Electronic structure and charge order in square planar low valence nickelates
Des biscuits seront offerts dans la cuisinette de l’IQ dès 10h30, heure à partir de laquelle le café sera gratuit jusqu’à 11h00. Le séminaire débutera à 11h00. Venez en grand nombre!
Cookies will be available in the IQ kitchenette starting at 10:30, at which time coffee will be free until 11:00. Talk starts at 11:00. A nice occasion to discuss!À l'atrium D9 et sur Zoom
Condensed Matter Physics and Materials Science Department, Brookhaven National Laboratory
The discovery of superconductivity in square planar low valence nickelates has ignited a vigorous debate regarding their essential electronic properties: Do these materials have appreciable oxygen charge-transfer character and superexchange akin to the cuprates or are they in a distinct Mott-Hubbard regime where oxygen plays a minimal role and superexchange is negligible? Do they host charge order as cuprates and what is the electronic character of this symmetry breaking? Here, we resolve these questions using O K-edge and Ni L-edge RIXS measurements of the low valance nickelate La4Ni3O8 and a prototypical cuprate La2−xSrxCuO4 (x=0.35), interpreting the results with exact diagonalization calculations [1,2]. As expected, the cuprate lies deep in the charge-transfer regime of the Zaanen-Sawatzky-Allen (ZSA) scheme. The nickelate, however, is not well-described by either limit of the ZSA scheme and is found to be of mixed charge-transfer / Mott-Hubbard character with the Coulomb repulsion U of similar size to the charge trans-fer energy Δ. Nevertheless, the transition-metal-oxygen hopping is larger in La4Ni3O8 than in La2−xSrxCuO4, which leads to a significant superexchange interaction of J~70 meV and an appreciable hole occupation of the ligand O orbitals in La4Ni3O8 despite its larger Δ. Moreover, we identify intertwined involvements of Ni 3𝑑𝑑𝑥𝑥2−𝑦𝑦2, 3𝑑𝑑3𝑧𝑧2−𝑟𝑟2, and O 2𝑝𝑝𝜎𝜎 orbitals in its formation of diagonal charge order. More specifically, the Ni 3𝑑𝑑𝑥𝑥2−𝑦𝑦2 orbitals, strongly hybridized with planar O 2𝑝𝑝𝜎𝜎, largely shape the spatial charge distribution and lead to Ni site-centered charge order. The 3𝑑𝑑3𝑧𝑧2−𝑟𝑟2 orbitals play a small, but non-negligible role in the charge order as they hybridize with the rare-earth 5d orbitals. Our results clarify the essential characteristics of low valence nickelates and put strong constraints on theoretical interpretations of superconductivity in these materials.
 J. Q. Lin et al., Phys. Rev. Lett. 126, 087001 (2021).
 Y. Shen et al., Phys. Rev. X 12, 011055 (2022)
ID de réunion : 886 4716 7648
Code secret : 1368
Invité de Stefanos Kourtis