dd excitations in three-dimensional q-space: A nonresonant inelastic X-ray scattering study on NiO

¹ National Synchrotron Radiation Research Center (NSRRC) - Hsinchu 30076, Taiwan
² Japan Synchrotron Radiation Research Institute (JASRI) - Kouto 1-1-1, Sayo, Hyogo 679-5198, Japan
³ National Synchrotron Light Source II, Brookhaven National Laboratory - Upton, NY 11973, USA
⁴ Max Planck Institute Stuttgart - Heisenbergstrasse 1, 70569 Stuttgart, Germany, EU
⁵ Institute of Physics, Academia Sinica - Nankang, Taipei 11529, Taiwan
⁶ Condensed Matter Physics and Materials Science Department, Brookhaven National Laboratory Upton, NY 11973, USA

^a hiraoka@spring8.or.jp

Received: 13 July 2011
Accepted: 8 September 2011

Abstract

We have studied the dd excitations in NiO over three-dimensional momentum (q) space using nonresonant inelastic X-ray scattering. In addition to the previously reported peaks at 1.7 and 3.0 eV, another peak is found at 1.0 eV, with a dramatically different intensity distribution in momentum space.Contrary to the other two peaks that form oval structures maximizing at [111] directions, the 1.0 eV peak displays appreciable intensity along low-symmetry axes near [311] and [210], but vanishes in the three principal axes [100], [110], and [111], indicating a significant difference in the exciton wave function.We find good agreement between the experimental data and two state-of-the-art theories, advocating investigating other strongly correlated materials with similar experimental/theoretical approaches.