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We have studied the electronic properties of the ladder compound α ′ -NaV 2 O 5 adopting a joint experimental and theoretical approach. The momentumdependent loss function was measured using electron energy-loss spectroscopy in transmission. The optical conductivity derived from the loss function by a Kramers-Kronig analysis agrees well with our results from LSDA+U bandstructure calculations upon application of an antiferromagnetic alignment of the V 3d xy spins along the legs and an on-site Coulomb interaction U of between 2 and 3 eV. The decomposition of the calculated optical conductivity into contributions from transitions between selected energy regions of the DOS reveals the origin of the observed anisotropy of the optical conductivity. In addition, we have investigated the plasmon excitations related to transitions between the vanadium states within an effective 16 site vanadium cluster model. Good agreement between the theoretical and experimental loss function was obtained using the hopping parameters derived from the tight binding fit to the band-structure and moderate Coulomb interactions between 1 the electrons within the ab plane.

The dynamics of a hole in a CuO4 plaquette: electron energy-loss spectroscopy of Li2CuO2 Atzkern, S.; Knupfer, M.; Golden, M.S.; Fink, J.; Waidacher, C.; Richter, J.; Becker, K.W.; Motoyama, N.; Eisaki, H. Published in:Physical Review B DOI:10.1103/PhysRevB.62.7845 Link to publication Citation for published version (APA):Atzkern, S., Knupfer, M., Golden, M. S., Fink, J., Waidacher, C., Richter, J., ... Eisaki, H. (2000). The dynamics of a hole in a CuO4 plaquette: electron energy-loss spectroscopy of Li2CuO2. Physical Review B, 62, 7845-7849. DOI: 10.1103/PhysRevB.62.7845 General rightsIt is not permitted to download or to forward/distribute the text or part of it without the consent of the author(s) and/or copyright holder(s), other than for strictly personal, individual use, unless the work is under an open content license (like Creative Commons). Disclaimer/Complaints regulationsIf you believe that digital publication of certain material infringes any of your rights or (privacy) interests, please let the Library know, stating your reasons. In case of a legitimate complaint, the Library will make the material inaccessible and/or remove it from the website. Please Ask the Library: http://uba.uva.nl/en/contact, or a letter to: Library of the University of Amsterdam, Secretariat, Singel 425, 1012 WP Amsterdam, The Netherlands. You will be contacted as soon as possible. We have measured the energy-and momentum-dependent loss function of Li 2 CuO 2 single crystals by means of electron energy-loss spectroscopy in transmission. Using the same values for the model parameters, the low-energy features of the spectrum as well as published Cu 2p 3/2 x-ray photoemission data of Li 2 CuO 2 are well described by a cluster model that consists of a single CuO 4 plaquette only. This demonstrates that charge excitations in Li 2 CuO 2 are strongly localized.

Valence band excitations in V2O5Atzkern, S.; Borisenko, S.V.; Knupfer, M.; Golden, M.S.; Fink, J.; Yaresko, A.N.; Antonov, V.N.; Klemm, M.; Horn, S. General rightsIt is not permitted to download or to forward/distribute the text or part of it without the consent of the author(s) and/or copyright holder(s), other than for strictly personal, individual use, unless the work is under an open content license (like Creative Commons). Disclaimer/Complaints regulationsIf you believe that digital publication of certain material infringes any of your rights or (privacy) interests, please let the Library know, stating your reasons. In case of a legitimate complaint, the Library will make the material inaccessible and/or remove it from the website. Please Ask the Library: http://uba.uva.nl/en/contact, or a letter to: Library of the University of Amsterdam, Secretariat, Singel 425, 1012 WP Amsterdam, The Netherlands. You will be contacted as soon as possible. We present a joint theoretical and experimental investigation of the electronic and optical properties of vanadium pentoxide. Electron energy-loss spectroscopy in transmission was employed to measure the momentum-dependent loss function. This in turn was used to derive the optical conductivity, which is compared to the results of band-structure calculations. A good qualitative and quantitative agreement between the theoretical and the experimental optical conductivity was observed. The experimentally observed anisotropy of the optical properties of V 2 O 5 could be understood in the light of an analysis of the theoretical data involving the decomposition of the calculated optical conductivity into contributions from transitions into selected energy regions of the conduction band. In addition, based upon a tight binding fit to the band structure, values are given for the effective V 3d xy -O 2p hopping terms and are compared to the corresponding values for ␣Ј-NaV 2 O 5 .

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