Open this publication in new window or tab >>2007 (English)Doctoral thesis, comprehensive summary (Other scientific)
Abstract [en]
The work presented in this thesis aims at achieving an increased understanding of the electronic structure of materials whose properties are to a large extent governed by transition metals. All studies are based on data from angle-resolved photoelectron spectroscopy (ARPES) employed on the valence band of the studied systems. In some cases spectroscopic data have also been combined with numerical electronic structure studies performed using a density functional theory computer code.
Five of the studies make extensive use of the benefits provided by performing angle-resolved photoelectron spectroscopy at high photon energies. When probed with soft x-ray photons, the near Fermi edge distribution of spectral weight in Nd2-xCexCuO4 and La2-x-yNdySrxCuO4 display significant differences as compared to similar studies performed in the 20-100 eV range of photon energies. This effect can be attributed to the approximate two-fold increase in probing depth as compared to the low photon energy case.
However, high photon energies not only give increased probing depth, it also enables a straightforward interpretation of ARPES data from fully three-dimensional compounds in terms of valence band energy dispersion. This principle has been used to study the dispersions in the transition metal oxides CoO and Cu2O as well as in a proof-of-principle study, where copper was used as a test case.
CoO exhibits a magnetic phase transition at the Néel temperature, from a paramagnetic state into an antiferromagnetically ordered state. The presented data show a significant shift of spectral weight between different band structure regions as the sample temperature is elevated across the Néel temperature.
The Cu2O ARPES data have confirmed the existence of a hybridized Cu 3d - Cu 4s state. Through comparision with theoretically calculated results, a refined value of the Hubbard potential U has been determined.
An extensive ARPES dataset from copper, covering the entire Brillouin zone, has in a proof-of-principle study been used to derive the binding-energy resolved valence band charge density.
Two ARPES studies of the La2-x-yNdySrxCuO4 system have been performed in the cnventional low photon energy range. The high energy resolution has enabled a detailed study of dispersive features in the near Fermil level region of the valence band.
Place, publisher, year, edition, pages
Stockholm: KTH, 2007. p. x, 38
Series
Trita-ICT/MAP ; 2007:9
Keywords
angle-resolved photoelectron spectroscopy, electronic structure, oxides, high-temperature superconductors
National Category
Other Engineering and Technologies not elsewhere specified
Identifiers
urn:nbn:se:kth:diva-4568 (URN)978-91-7178-783-5 (ISBN)
Public defence
2007-12-11, Sal N2, KTH-Electrum 3, Isafjordsgatan 28 A/D, Kista, 10:00
Opponent
Supervisors
2007-12-072007-12-072022-06-26Bibliographically approved