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Investigations of Transition Metal Systems: Angle-Resolved Photoelectron Spectroscopy at Low and High Energy
KTH, School of Information and Communication Technology (ICT), Material Physics, Material Physics, MF.
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. , x, 38 p.
Series
Trita-ICT/MAP, 2007:9
Keyword [en]
angle-resolved photoelectron spectroscopy, electronic structure, oxides, high-temperature superconductors
National Category
Other Engineering and Technologies not elsewhere specified
Identifiers
URN: urn:nbn:se:kth:diva-4568ISBN: 978-91-7178-783-5 (print)OAI: oai:DiVA.org:kth-4568DiVA: diva2:12893
Public defence
2007-12-11, Sal N2, KTH-Electrum 3, Isafjordsgatan 28 A/D, Kista, 10:00
Opponent
Supervisors
Available from: 2007-12-07 Created: 2007-12-07 Last updated: 2010-07-02Bibliographically approved
List of papers
1. Angle Resolved Photoemission from Nd(1.85)Ce(0.15)CuO(4) using High Energy Photons: A Fermi Surface Investigation
Open this publication in new window or tab >>Angle Resolved Photoemission from Nd(1.85)Ce(0.15)CuO(4) using High Energy Photons: A Fermi Surface Investigation
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2004 (English)In: Physical Review Letters, ISSN 0031-9007, Vol. 93, no 13, 136402-1-136402-4 p.Article in journal (Refereed) Published
Abstract [en]

We have performed an angle resolved photoemission study on a single crystal of the optimally electron doped (n-type) cuprate superconductor Nd2-xCexCuO4 (x=0.15) at a photon energy of 400 eV. The Fermi surface is mapped out and is, in agreement with earlier measurements, of hole-type with the expected Luttinger volume. However, comparing with previous low energy measurements, we observe a different Fermi surface shape and a different distribution of spectral intensity around the Fermi surface contour. The observed Fermi surface shape indicates a stronger electron correlation in the bulk as compared to the surface.

Keyword
Antiferromagnetism; Doping (additives); Electric power measurement; Electron energy analyzers; Electronic structure; Electrons; Fermi surface; Neodymium compounds; Oxide superconductors; Photons; Single crystals; Synchrotron radiation
National Category
Condensed Matter Physics Other Engineering and Technologies not elsewhere specified
Identifiers
urn:nbn:se:kth:diva-8058 (URN)10.1103/PhysRevLett.93.136402 (DOI)000224131400061 ()2-s2.0-19644397887 (Scopus ID)
Note
QC 20100702 QC 20110916Available from: 2007-12-12 Created: 2007-12-12 Last updated: 2011-09-16Bibliographically approved
2. The electronic structure of La(1.48)Nd(0.4)Sr(0.12)CuO(4) probed by high- and low-energy angle-resolved photoelectron spectroscopy: Evolution with probing depth
Open this publication in new window or tab >>The electronic structure of La(1.48)Nd(0.4)Sr(0.12)CuO(4) probed by high- and low-energy angle-resolved photoelectron spectroscopy: Evolution with probing depth
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2009 (English)In: Physical Review B Condensed Matter, ISSN 0163-1829, E-ISSN 1095-3795, Vol. 80, no 9, 094503-1-094503-6 p.Article in journal (Refereed) Published
Abstract [en]

We present angle-resolved photoelectron spectroscopy data probing the electronic structure of the Nd-substituted high-T-c cuprate La1.48Nd0.4Sr0.12CuO4. Data have been acquired at low and high photon energies, h nu=55 and 500 eV, respectively. The two extracted Fermi surfaces show significant differences. The differences can be attributed to either the change in probing depth suggesting dissimilarity of the intrinsic electronic structure between surface and bulk regions, or a considerable c-axis dispersion signaling a strong interlayer coupling. At both photon energies, considerable spectral weight is observed at all points along the Fermi surface and the intensity distribution as well as Fermi-surface shape observed at low as well as high photon energy is markedly different from what has been previously reported for La1.28Nd0.6Sr0.12CuO4 by Zhou [Science 286, 268 (1999)]. Document Type: Article

Keyword
band structure; Fermi surface; high-temperature superconductors; lanthanum compounds; neodymium; photoelectron spectra; strontium compounds
National Category
Other Engineering and Technologies not elsewhere specified
Identifiers
urn:nbn:se:kth:diva-8059 (URN)10.1103/PhysRevB.80.094503 (DOI)000270383000073 ()2-s2.0-70349974665 (Scopus ID)
Note
QC 20100702Available from: 2007-12-12 Created: 2007-12-12 Last updated: 2010-07-02Bibliographically approved
3. Transfer of spectral weight across the magnetic transition in CoO: novel results from high-energy angle-resolved photoelectron spectroscopy
Open this publication in new window or tab >>Transfer of spectral weight across the magnetic transition in CoO: novel results from high-energy angle-resolved photoelectron spectroscopy
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(English)Manuscript (preprint) (Other academic)
National Category
Other Engineering and Technologies not elsewhere specified
Identifiers
urn:nbn:se:kth:diva-13915 (URN)
Note
QC 20100702Available from: 2010-07-02 Created: 2010-07-02 Last updated: 2010-07-02Bibliographically approved
4. Probing the valence band structure of Cu2O using high-energy angle-resolved photoelectron spectroscopy
Open this publication in new window or tab >>Probing the valence band structure of Cu2O using high-energy angle-resolved photoelectron spectroscopy
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2007 (English)In: Physical Review B Condensed Matter, ISSN 0163-1829, E-ISSN 1095-3795, Vol. 76, no 11, 115127-1-115127-7 p.Article in journal (Refereed) Published
Abstract [en]

We present angle-resolved photoemission data along the M-Gamma-M direction from a Cu2O(111) single crystal, collected at high photon energies (h nu=619 and 891 eV) and T=100 K. Because of the high photon energies and effective background subtraction, our data give a clear picture of the bulk band structure. The results confirm the existence of a hybridized Cu 3d-Cu 4s state located between the two main Cu 3d and O 2p band regions. Several theoretical studies have predicted the existence of this band, but until now it has not been detected in any photoemission measurements. The experimentally derived band structure is compared to local density approximation calculations with and without the Hubbard potential U. The clear band dispersion in our experimental data has enabled us to extract a refined Hubbard U value, which makes it possible to achieve a better agreement between theoretically calculated bands and experimental data.

Keyword
CLOSED-SHELL INTERACTIONS; ELECTRONIC-STRUCTURE; SYNCHROTRON-RADIATION; POLAR COVALENCES; CUPROUS-OXIDE; DIRECT IMAGES; PHOTOEMISSION; CUPRITE; CUO; SPECTRA
National Category
Other Engineering and Technologies not elsewhere specified
Identifiers
urn:nbn:se:kth:diva-8063 (URN)10.1103/PhysRevB.76.115127 (DOI)000249786400046 ()2-s2.0-34848905947 (Scopus ID)
Note
QC 20100702Available from: 2007-12-12 Created: 2007-12-12 Last updated: 2012-03-20Bibliographically approved
5. Revealing the charge density in solids
Open this publication in new window or tab >>Revealing the charge density in solids
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(English)Manuscript (Other academic)
National Category
Other Engineering and Technologies not elsewhere specified
Identifiers
urn:nbn:se:kth:diva-8062 (URN)
Note
QC 20100702Available from: 2007-12-12 Created: 2007-12-12 Last updated: 2010-07-02Bibliographically approved
6. Experimental evidence of a quantum phase transition in La(2-x)Sr(x)CuO4()
Open this publication in new window or tab >>Experimental evidence of a quantum phase transition in La(2-x)Sr(x)CuO4()
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(English)Manuscript (Other academic)
National Category
Other Engineering and Technologies not elsewhere specified
Identifiers
urn:nbn:se:kth:diva-8067 (URN)
Note
QC 20100702Available from: 2007-12-12 Created: 2007-12-12 Last updated: 2010-08-10Bibliographically approved

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