title: Ground-state oxygen holes and the metal-insulator transition in the negative charge-transfer rare-earth nickelates.
abstract: The metal-insulator transition and the intriguing physical properties of rare-earth perovskite nickelates have attracted considerable attention in recent years. Nonetheless, a complete understanding of these materials remains elusive. Here we combine X-ray absorption and resonant inelastic X-ray scattering (RIXS) spectroscopies to resolve important aspects of the complex electronic structure of rare-earth nickelates, taking NdNiO3thin film as representative example. The unusual coexistence of bound and continuum excitations observed in the RIXS spectra provides strong evidence for abundant oxygen holes in the ground state of these materials. Using cluster calculations and Anderson impurity model interpretation, we show that distinct spectral signatures arise from a Ni 3d8configuration along with holes in the oxygen 2p valence band, confirming suggestions that these materials do not obey a conventional positive charge-transfer picture, but instead exhibit a negative charge-transfer energy in line with recent models interpreting the metal-insulator transition in terms of bond disproportionation.
authors.affiliation: Research Department Synchrotron Radiation and Nanotechnology, Paul Scherrer Institut, CH-5232 Villigen PSI, Switzerland.|National Synchrotron Light Source II, Brookhaven National Laboratory, Upton, New York 11973, USA.
authors.forename: Valentina
authors.initials: V
authors.lastname: Bisogni
authors.affiliation: Department of Quantum Matter Physics, University of Geneva, 24 Quai Ernest-Ansermet, 1211 Geneva 4, Switzerland.
authors.forename: Sara
authors.initials: S
authors.lastname: Catalano
authors.affiliation: Department of Physics and Astronomy, University of British Columbia, Vancouver, British Columbia, Canada V6T 1Z1.|Quantum Matter Institute, University of British Columbia, Vancouver, British Columbia, Canada V6T 1Z4.
authors.forename: Robert J
authors.initials: RJ
authors.lastname: Green
authors.affiliation: Department of Quantum Matter Physics, University of Geneva, 24 Quai Ernest-Ansermet, 1211 Geneva 4, Switzerland.
authors.forename: Marta
authors.initials: M
authors.lastname: Gibert
authors.affiliation: Department of Quantum Matter Physics, University of Geneva, 24 Quai Ernest-Ansermet, 1211 Geneva 4, Switzerland.
authors.forename: Raoul
authors.initials: R
authors.lastname: Scherwitzl
authors.affiliation: Research Department Synchrotron Radiation and Nanotechnology, Paul Scherrer Institut, CH-5232 Villigen PSI, Switzerland.|Beijing National Laboratory for Condensed Matter Physics, and Institute of Physics, Chinese Academy of Sciences, Beijing 100190, China.
authors.forename: Yaobo
authors.initials: Y
authors.lastname: Huang
authors.affiliation: Research Department Synchrotron Radiation and Nanotechnology, Paul Scherrer Institut, CH-5232 Villigen PSI, Switzerland.
authors.forename: Vladimir N
authors.initials: VN
authors.lastname: Strocov
authors.affiliation: Department of Quantum Matter Physics, University of Geneva, 24 Quai Ernest-Ansermet, 1211 Geneva 4, Switzerland.|London Centre for Nanotechnology and Department of Physics and Astronomy, University College London, 17-19 Gordon Street, London WC1H 0HA, UK.
authors.forename: Pavlo
authors.initials: P
authors.lastname: Zubko
authors.affiliation: Department of Physics and Astronomy, University of British Columbia, Vancouver, British Columbia, Canada V6T 1Z1.
authors.forename: Shadi
authors.initials: S
authors.lastname: Balandeh
authors.affiliation: Department of Quantum Matter Physics, University of Geneva, 24 Quai Ernest-Ansermet, 1211 Geneva 4, Switzerland.
authors.forename: Jean-Marc
authors.initials: JM
authors.lastname: Triscone
authors.affiliation: Department of Physics and Astronomy, University of British Columbia, Vancouver, British Columbia, Canada V6T 1Z1.|Quantum Matter Institute, University of British Columbia, Vancouver, British Columbia, Canada V6T 1Z4.
authors.forename: George
authors.initials: G
authors.lastname: Sawatzky
authors.affiliation: Research Department Synchrotron Radiation and Nanotechnology, Paul Scherrer Institut, CH-5232 Villigen PSI, Switzerland.
authors.forename: Thorsten
authors.initials: T
authors.lastname: Schmitt