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Phys. Rev. Lett. 99, 026401 (2007) [4 pages]

Nonresonant Inelastic X-Ray Scattering and Energy-Resolved Wannier Function Investigation of d-d Excitations in NiO and CoO

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B. C. Larson1, Wei Ku2, J. Z. Tischler1, Chi-Cheng Lee2,3, O. D. Restrepo1,4, A. G. Eguiluz1,4, P. Zschack5, and K. D. Finkelstein6
1Materials Science & Technology Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831, USA
2Department of Physics, Brookhaven National Laboratory, Upton, New York, 11973, USA
3Department of Physics, Tamkang University, Tamsui, Taiwan 25137, Republic of China
4Department of Physics & Astronomy, University of Tennessee, Knoxville, Tennessee 37996, USA
5XOR/UNI, Advanced Photon Source, Argonne National Laboratory, Argonne, Illinois 60439, USA
6Cornell High Energy Synchrotron Source, Cornell University, Ithaca, New York 14853, USA

Received 19 January 2007; published 10 July 2007

Nonresonant inelastic x-ray scattering measurements on NiO and CoO show that strong dipole-forbidden d-d excitations appear within the Mott gap at large wave vectors. These dominant excitations are highly anisotropic, and have [001] nodal directions for NiO. Theoretical analyses based on a novel, energy-resolved Wannier function (within the local density approximation+Hubbard   U) show that the anisotropy reflects the local exciton wave functions and local point-group symmetry. The sensitivity to weak symmetry breaking in particle-hole wave functions suggests a wide application to strongly correlated systems.

© 2007 The American Physical Society

URL:
http://link.aps.org/doi/10.1103/PhysRevLett.99.026401
DOI:
10.1103/PhysRevLett.99.026401
PACS:
71.27.+a, 61.10.Eq, 71.15.−m, 71.35.−y
 
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