Physical Review Letters ( IF 8.385 ) Pub Date : 2021-02-22 , DOI: 10.1103/physrevlett.126.087001
J. Q. Lin; P. Villar Arribi; G. Fabbris; A. S. Botana; D. Meyers; H. Miao; Y. Shen; D. G. Mazzone; J. Feng; S. G. Chiuzbăian; A. Nag; A. C. Walters; M. García-Fernández; Ke-Jin Zhou; J. Pelliciari; I. Jarrige; J. W. Freeland; Junjie Zhang; J. F. Mitchell; V. Bisogni; X. Liu; M. R. Norman; M. P. M. Dean

The discovery of superconductivity in a ${d}^{9-\delta }$ nickelate has inspired disparate theoretical perspectives regarding the essential physics of this class of materials. A key issue is the magnitude of the magnetic superexchange, which relates to whether cuprate-like high-temperature nickelate superconductivity could be realized. We address this question using Ni $L$-edge and O $K$-edge spectroscopy of the reduced ${d}^{9-1/3}$ trilayer nickelates ${R}_{4}{\mathrm{Ni}}_{3}{\mathrm{O}}_{8}$ (where $R=\mathrm{La}$, Pr) and associated theoretical modeling. A magnon energy scale of $\sim 80\text{\hspace{0.17em}}\text{\hspace{0.17em}}\mathrm{meV}$ resulting from a nearest-neighbor magnetic exchange of $J=69\left(4\right)\text{\hspace{0.17em}}\text{\hspace{0.17em}}\mathrm{meV}$ is observed, proving that ${d}^{9-\delta }$ nickelates can host a large superexchange. This value, along with that of the Ni-O hybridization estimated from our O $K$-edge data, implies that trilayer nickelates represent an intermediate case between the infinite-layer nickelates and the cuprates. Layered nickelates thus provide a route to testing the relevance of superexchange to nickelate superconductivity.

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