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Novel Electronic Behavior Driving NdNiO3 Metal-Insulator Transition

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journal contribution
posted on 05.11.2015 by MH Upton, Y. Choi, H. Park, J. Liu, D. Meyers, J. Chakhalian, S. Middey, J-W Kim, PJ Ryan
We present evidence that the metal-insulator transition (MIT) in a tensile-strained NdNiO3 (NNO) film is facilitated by a redistribution of electronic density and that it neither requires Ni charge disproportionation nor a symmetry change [U. Staub et al., Phys. Rev. Lett. 88, 126402 (2002); R. Jaramillo et al., Nat. Phys. 10, 304 (2014)]. Given that epitaxial tensile strain in thin NNO films induces preferential occupancy of the eg dx2−y2 orbital we propose that the larger transfer integral of this orbital state with the O 2p orbital state mediates a redistribution of electronic density from the Ni atom. A decrease in the Ni dx2−y2 orbital occupation is directly observed by resonant inelastic x-ray scattering below the MIT temperature. Furthermore, an increase in the Nd charge occupancy is measured by x-ray absorption at the Nd L3 edge. Both spin-orbit coupling and crystal field effects combine to break the degeneracy of the Nd 5d states, shifting the energy of the Nd eg dx2−y2 orbit towards the Fermi level, allowing the A site to become an active acceptor during the MIT. This work identifies the relocation of electrons from the Ni 3d to the Nd 5d orbitals across the MIT. We propose that the insulating gap opens between the Ni 3d and O 2p states, resulting from Ni 3d electron localization. The transition seems to be neither a purely Mott-Hubbard transition nor a simple charge transfer.

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Work at the Advanced Photon Source is supported by the U.S. Department of Energy, Office of Science under Grant No. DEAC02-06CH11357. J. C., D. M. and S. M. were supported by DOD-ARO under the Grant No. 0402-17291. H. Park gratefully acknowledges the support of start-up funds from UIC and ANL. H. P. also acknowledges the computing resources provided on Blues, a high-performance computing cluster operated by the Laboratory Computing Resource Center at Argonne National Laboratory.

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Publisher Statement

This is the copy of an article published in Physical Review Letters © 2015 American Physical Society Publications.

Publisher

American Physical Society

issn

0031-9007

Issue date

13/07/2015

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