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  • 1.
    Berntsen, Magnus H.
    et al.
    KTH, School of Information and Communication Technology (ICT), Material Physics, Material Physics, MF.
    Götberg, Olof
    KTH, School of Information and Communication Technology (ICT), Material Physics, Material Physics, MF.
    Tjernberg, Oscar
    KTH, School of Information and Communication Technology (ICT), Material Physics, Material Physics, MF.
    An experimental setup for high resolution 10.5 eV laser-based angle-resolved photoelectron spectroscopy using a time-of-flight electron analyzer2011In: Review of Scientific Instruments, ISSN 0034-6748, E-ISSN 1089-7623, Vol. 82, no 9, p. 095113-Article in journal (Refereed)
    Abstract [en]

    We present an experimental setup for laser-based angle-resolved time-of-flight photoemission. Using a picosecond pulsed laser, photons of energy 10.5 eV are generated through higher harmonic generation in xenon. The high repetition rate of the light source, variable between 0.2 and 8 MHz, enables high photoelectron count rates and short acquisition times. By using a time-of-flight analyzer with angle-resolving capabilities, electrons emitted from the sample within a circular cone of up to +/- 15 degrees can be collected. Hence, simultaneous acquisition of photoemission data for a complete area of the Brillouin zone is possible. The current photon energy enables bulk sensitive measurements, high angular resolution, and the resulting covered momentum space is large enough to enclose the entire Brillouin zone in cuprate high-T(c) superconductors. Fermi edge measurements on polycrystalline Au shows an energy resolution better than 5 meV. Data from a test measurement of the Au(111) surface state are presented along with measurements of the Fermi surface of the high-T(c) superconductor Bi(2)Sr(2)CaCu(2)O(8+delta) (Bi2212).

  • 2.
    Berntsen, Magnus H.
    et al.
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Material Physics, MF.
    Götberg, Olof
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Material Physics, MF.
    Wojek, Bastian M.
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Material Physics, MF.
    Tjernberg, Oscar
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Material Physics, MF.
    Direct observation of decoupled Dirac states at the interface between topological and normal insulators2013In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 88, no 19, article id 195132Article in journal (Refereed)
    Abstract [en]

    Several proposed applications and exotic effects in topological insulators rely on the presence of helical Dirac states at the interface between a topological insulator and a normal insulator. In the present work, we have used low-energy angle-resolved photoelectron spectroscopy to uncover and characterize the interface states of Bi2Se3 thin films and Bi2Te3/Bi2Se3 heterostructures grown on Si(111). The results establish that Dirac fermions are indeed present at the topological-normal-insulator boundary and absent at the topological-topological-insulator interface. Moreover, it is demonstrated that band bending present within the topological-insulator films leads to a substantial separation of the interface and surface states in energy. These results pave the way for further studies and the realization of interface-related phenomena in topological-insulator thin-film heterostructures.

  • 3.
    Berntsen, Magnus H.
    et al.
    KTH, School of Information and Communication Technology (ICT), Material Physics, Material Physics, MF.
    Palmgren, P.
    Leandersson, M.
    Hahlin, A.
    Åhlund, J.
    Wannberg, B.
    Mansson, M.
    Tjernberg, Oscar
    KTH, School of Information and Communication Technology (ICT), Material Physics, Material Physics, MF.
    A spin- and angle-resolving photoelectron spectrometer2010In: Review of Scientific Instruments, ISSN 0034-6748, E-ISSN 1089-7623, Vol. 81, no 3Article in journal (Refereed)
    Abstract [en]

    A new type of hemispherical electron energy analyzer that permits angle and spin resolved photoelectron spectroscopy has been developed. The analyzer permits standard angle resolved spectra to be recorded with a two-dimensional detector in parallel with spin detection using a mini-Mott polarimeter. General design considerations as well as technical solutions are discussed and test results from the Au(111) surface state are presented.

  • 4. Brookes, N. B.
    et al.
    Ghiringhelli, G.
    Tjernberg, Oscar
    KTH, Superseded Departments, Microelectronics and Information Technology, IMIT.
    Tjeng, L. H.
    Mizokawa, T.
    Li, T. W.
    Menovsky, A. A.
    Detection of Zhang-Rice singlets using spin-polarized photoemission2001In: Physical Review Letters, ISSN 0031-9007, E-ISSN 1079-7114, Vol. 8723, no 23Article in journal (Refereed)
    Abstract [en]

    From a spin-resolved photoemission study on the Bi2Sr2CaCu2O8+delta superconductor, we show experimentally that the first ionization state is of nearly pure singlet character. This is true both above and below the superconducting transition and in the presence of doping and band formation. This provides direct support for the existence and stability of Zhang-Rice singlets in high-temperature superconductors, justifying the ansatz of single-band models. Moreover, we establish this technique as an important probe for a wide range of cuprates and strongly correlated materials.

  • 5. Chang, J.
    et al.
    Månsson, Martin
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Material Physics, MF.
    Pailhes, S.
    Claesson, Thomas
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Material Physics, MF.
    Lipscombe, O. J.
    Hayden, S. M.
    Patthey, L.
    Tjernberg, Oscar
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Material Physics, MF.
    Mesot, J.
    Anisotropic breakdown of Fermi liquid quasiparticle excitations in overdoped La2-xSrxCuO42013In: Nature Communications, ISSN 2041-1723, E-ISSN 2041-1723, Vol. 4, p. 2559-Article in journal (Refereed)
    Abstract [en]

    High-temperature superconductivity emerges from an un-conventional metallic state. This has stimulated strong efforts to understand exactly how Fermi liquids breakdown and evolve into an un-conventional metal. A fundamental question is how Fermi liquid quasiparticle excitations break down in momentum space. Here we show, using angle-resolved photoemission spectroscopy, that the Fermi liquid quasiparticle excitations of the overdoped superconducting cuprate La1.77Sr0.23CuO4 is highly anisotropic in momentum space. The quasiparticle scattering and residue behave differently along the Fermi surface and hence the Kadowaki-Wood's relation is not obeyed. This kind of Fermi liquid breakdown may apply to a wide range of strongly correlated metal systems where spin fluctuations are present.

  • 6. Chang, J.
    et al.
    Sassa, Y.
    Guerrero, S.
    Mansson, M.
    Shi, M.
    Pailhes, S.
    Bendounan, A.
    Mottl, R.
    Claesson, T.
    Tjernberg, Oscar
    KTH, School of Information and Communication Technology (ICT), Microelectronics and Information Technology, IMIT.
    Patthey, L.
    Ido, M.
    Oda, M.
    Momono, N.
    Mudry, C.
    Mesot, J.
    Electronic structure near the 1/8-anomaly in La-based cuprates2008In: New Journal of Physics, ISSN 1367-2630, E-ISSN 1367-2630, Vol. 10Article in journal (Refereed)
    Abstract [en]

    We report an angle-resolved photoemission study of the electronic structure of the pseudogap state in La1.48Nd0.4Sr0.12CuO4 (T-c < 7 K). Two opposite dispersing Fermi arcs are the main result of this study. Several scenarios that can explain this observation are discussed.

  • 7.
    Chang, Johan
    et al.
    Laboratory for Neutron Scattering, ETH Zurich and Paul Scherrer Institute, Villigen.
    Pailhés, Stephane
    Laboratory for Neutron Scattering, ETH Zurich and Paul Scherrer Institute, Villigen.
    Shi, Ming
    Swiss Light Source, Paul Scherrer Institute, Villigen.
    Månsson, Martin
    KTH, School of Information and Communication Technology (ICT), Material Physics.
    Claesson, Thomas
    KTH, School of Information and Communication Technology (ICT), Material Physics.
    Tjernberg, Oscar
    KTH, School of Information and Communication Technology (ICT), Material Physics.
    Voigt, Jörg
    Institute for Solid State Research, Forschungszentrum Jülich.
    Perez, V.
    Swiss Light Source, Paul Scherrer Institute, Villigen.
    Patthey, Luc
    Swiss Light Source, Paul Scherrer Institute, Villigen.
    Momono, Naoki
    Department of Physics, Hokkaido University, Sapporo.
    Oda, Migaku
    Department of Physics, Hokkaido University, Sapporo.
    Ido, Masayuki
    Department of Physics, Hokkaido University, Sapporo.
    Schnyder, A.
    Condensed Matter Theory Group, Villigen.
    Mudry, C.
    Condensed Matter Theory Group, Villigen.
    Mesot, Joël
    Laboratory for Neutron Scattering, ETH Zurich and Paul Scherrer Institute, Villigen.
    When low- and high-energy electronic responses meet in cuprate superconductors2007In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 75, no 22, p. 224508-Article in journal (Refereed)
    Abstract [en]

    The existence of coherent quasiparticles near the Fermi energy in the low-temperature state of high-temperature superconductors has been well established by angle-resolved photoemission spectroscopy (ARPES). We present a study of La1.83Sr0.17CuO4 in the superconducting state and report an abrupt change in the quasiparticle spectral function, as we follow the dispersion of the ARPES signal from the Fermi energy to 0.6 eV. The interruption in the quasiparticle dispersion separates coherent quasiparticle peaks at low energies from broad incoherent excitations at high energies. We find that the boundary between these low-energy and high-energy features exhibits a cosine-shaped momentum dependence, reminiscent of the superconducting d-wave gap. Further intriguing similarities between characteristics of the incoherent excitations and quasiparticle properties suggest a close relation between the electronic response at high and low energies in cuprate superconductors.

  • 8.
    Chang, Johan
    et al.
    Laboratory for Neutron Scattering, ETH Zurich, Paul Scherrer Institute, Villigen.
    Shi, Ming
    Swiss Light Source, Paul Scherrer Institute, Villigen.
    Pailhés, Stephane
    Laboratory for Neutron Scattering, ETH Zurich, Paul Scherrer Institute, Villigen.
    Månsson, Martin
    KTH, School of Information and Communication Technology (ICT), Material Physics.
    Claesson, Thomas
    KTH, School of Information and Communication Technology (ICT), Material Physics.
    Tjernberg, Oscar
    KTH, School of Information and Communication Technology (ICT), Material Physics.
    Bendounan, Azzedin
    Laboratory for Neutron Scattering, ETH Zurich, Paul Scherrer Institute, Villigen.
    Sassa, Yasmine
    Laboratory for Neutron Scattering, ETH Zurich, Paul Scherrer Institute, Villigen.
    Patthey, Luc
    Swiss Light Source, Paul Scherrer Institute, Villigen.
    Momono, Naoki
    Department of Physics, Hokkaido University, Sapporo.
    Oda, Migaku
    Department of Physics, Hokkaido University, Sapporo.
    Ido, Masayuki
    Department of Physics, Hokkaido University, Sapporo.
    Guerrero, S.
    Condensed Matter Theory Group, Paul Scherrer Institute, Villigen.
    Mudry, C.
    Condensed Matter Theory Group, Paul Scherrer Institute, Villigen.
    Mesot, Joël
    Laboratory for Neutron Scattering, ETH Zurich, Paul Scherrer Institute, Villigen.
    Anisotropic quasiparticle scattering rates in slightly underdoped to optimally doped high-temperature La2-xSrxCuO4 superconductors2008In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 78, no 20, p. 205103-Article in journal (Refereed)
    Abstract [en]

    An angle-resolved photoemission study of the scattering rate in the superconducting phase of the high-temperature superconductor La2-xSrxCuO4 with x=0.145 and x=0.17, as a function of binding energy and momentum, is presented. We observe that the scattering rate scales linearly with binding energy up to the high-energy scale E-1 similar to 0.4 eV. The scattering rate is found to be strongly anisotropic, with a minimum along the (0,0)-(pi,pi) direction. A possible connection to a quantum-critical point is discussed.

  • 9.
    Claesson, Thomas
    et al.
    KTH, Superseded Departments, Microelectronics and Information Technology, IMIT.
    Månsson, Martin
    KTH, Superseded Departments, Microelectronics and Information Technology, IMIT.
    Dallera, Claudia
    INFM-Dipartimento di Fisica, Politecnico di Milano, Italy.
    Venturini, Federica
    Europ. Synchrt. Radiation Facility, Grenoble, France.
    De Nadaï, Celine
    Europ. Synchrt. Radiation Facility, Grenoble, France.
    Brookes, Nicholas B.
    Europ. Synchrt. Radiation Facility, Grenoble, France.
    Tjernberg, Oscar
    KTH, Superseded Departments, Microelectronics and Information Technology, IMIT.
    Angle Resolved Photoemission from Nd(1.85)Ce(0.15)CuO(4) using High Energy Photons: A Fermi Surface Investigation2004In: Physical Review Letters, ISSN 0031-9007, E-ISSN 1079-7114, Vol. 93, no 13, p. 136402-1-136402-4Article in journal (Refereed)
    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.

  • 10.
    Claesson, Thomas
    et al.
    KTH, School of Information and Communication Technology (ICT), Material Physics.
    Månsson, Martin
    KTH, School of Information and Communication Technology (ICT), Material Physics.
    Finazzi, M.
    Dallera, C.
    Cezar, J. C.
    Brookes, N. B.
    Tjernberg, Oscar
    KTH, School of Information and Communication Technology (ICT), Material Physics.
    Transfer of spectral weight across the magnetic transition in CoO: novel results from high-energy angle-resolved photoelectron spectroscopyManuscript (preprint) (Other academic)
  • 11.
    Claesson, Thomas
    et al.
    KTH, School of Information and Communication Technology (ICT), Material Physics.
    Månsson, Martin
    KTH, School of Information and Communication Technology (ICT), Material Physics.
    Önsten, Anneli
    KTH, School of Information and Communication Technology (ICT), Material Physics.
    Shi, Ming
    Swiss Light Source, Paul Scherrer Institut, Switzerland.
    Sassa, Yasmine
    Laboratory for Neutron Scattering, Zürich, Paul Scherrer Institut.
    Pailhés, Stephane
    Laboratory for Neutron Scattering, Zürich, Paul Scherrer Institut.
    Chang, Johan
    Laboratory for Neutron Scattering, Zürich, Paul Scherrer Institut.
    Bendounan, Azzedin
    Synchrotron SOLEIL, L'Orme des Merisiers, France.
    Patthey, Luc
    Swiss Light Source, Paul Scherrer Institut, Switzerland.
    Mesot, Joël
    Paul Scherrer Institute, ETH Zürich, Switzerland.
    Muro, Takayuki
    Japan Synchrotron Radiation Research Institute.
    Matsushita, Tomohiro
    Japan Synchrotron Radiation Research Institute.
    Kinoshita, Toyohiko
    Japan Synchrotron Radiation Research Institute.
    Nakamura, Tetsuya
    Japan Synchrotron Radiation Research Institute.
    Momono, Naoki
    Department of Physics, Hokkaido University, Japan.
    Oda, Migaku
    Department of Physics, Hokkaido University, Japan.
    Ido, Masayuki
    Department of Physics, Hokkaido University, Japan.
    Tjernberg, Oscar
    KTH, School of Information and Communication Technology (ICT), Material Physics.
    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 depth2009In: Physical Review B Condensed Matter, ISSN 0163-1829, E-ISSN 1095-3795, Vol. 80, no 9, p. 094503-1-094503-6Article in journal (Refereed)
    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

  • 12.
    Duan, Yu-Xia
    et al.
    Cent S Univ, Sch Phys & Elect, Changsha 410083, Hunan, Peoples R China..
    Zhang, Cheng
    Cent S Univ, Sch Phys & Elect, Changsha 410083, Hunan, Peoples R China..
    Rusz, Jan
    Uppsala Univ, Dept Phys & Astron, Box 516, S-75120 Uppsala, Sweden..
    Oppeneer, Peter M.
    Uppsala Univ, Dept Phys & Astron, Box 516, S-75120 Uppsala, Sweden..
    Durakiewicz, Tomasz
    Marie Curie Sklodowska Univ, Lnstitute Phys, PL-20031 Lublin, Poland..
    Sassa, Yasmine
    Uppsala Univ, Dept Phys & Astron, Box 516, S-75120 Uppsala, Sweden.;Chalmers Univ Technol, Dept Phys, S-41296 Gothenburg, Sweden..
    Tjernberg, Oscar
    KTH, School of Engineering Sciences (SCI), Applied Physics, Materials and Nanophysics.
    Månsson, Martin
    KTH, School of Engineering Sciences (SCI), Applied Physics, Materials and Nanophysics.
    Berntsen, Magnus H.
    KTH, School of Engineering Sciences (SCI), Applied Physics, Materials and Nanophysics.
    Wu, Fan-Ying
    Cent S Univ, Sch Phys & Elect, Changsha 410083, Hunan, Peoples R China..
    Zhao, Yin-Zou
    Cent S Univ, Sch Phys & Elect, Changsha 410083, Hunan, Peoples R China..
    Song, Jiao-Jiao
    Cent S Univ, Sch Phys & Elect, Changsha 410083, Hunan, Peoples R China..
    Wu, Qi-Yi
    Cent S Univ, Sch Phys & Elect, Changsha 410083, Hunan, Peoples R China..
    Luo, Yang
    Cent S Univ, Sch Phys & Elect, Changsha 410083, Hunan, Peoples R China..
    Bauer, Eric D.
    Los Alamos Natl Lab, Condensed Matter & Magnet Sci Grp, Los Alamos, NM 87545 USA..
    Thompson, Joe D.
    Los Alamos Natl Lab, Condensed Matter & Magnet Sci Grp, Los Alamos, NM 87545 USA..
    Meng, Jian-Qiao
    Cent S Univ, Sch Phys & Elect, Changsha 410083, Hunan, Peoples R China.;Hunan Normal Univ, SICQEA, Changsha 410081, Hunan, Peoples R China..
    Crystal electric field splitting and f-electron hybridization in heavy-fermion CePt2In72019In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 100, no 8, article id 085141Article in journal (Refereed)
    Abstract [en]

    We use high-resolution angle-resolved photoemission spectroscopy to investigate the electronic structure of the antiferromagnetic heavy fermion compound CePt2In7, which is amember of the CeIn3-derived heavy fermion material family. Weak hybridization among 4f electron states and conduction bands was identified in CePt2In7 at low temperature much weaker than that in the other heavy fermion compounds like CeIrIn5 and CeRhIn5. The Ce 4f spectrum shows fine structures near the Fermi energy, reflecting the crystal electric field splitting of the 4f(5/2)(1) and 4f(7/2)(1) states. Also, we find that the Fermi surface has a strongly three-dimensional topology, in agreement with density-functional theory calculations.

  • 13. Dziawa, P.
    et al.
    Kowalski, B. J.
    Dybko, K.
    Buczko, R.
    Szczerbakow, A.
    Szot, M.
    Lusakowska, E.
    Balasubramanian, T.
    Wojek, Bastian M.
    KTH, School of Information and Communication Technology (ICT), Material Physics (Closed 20120101), Material Physics, MF (Closed 20120101).
    Hårdensson Berntsen, Magnus
    KTH, School of Information and Communication Technology (ICT), Material Physics (Closed 20120101), Material Physics, MF (Closed 20120101).
    Tjernberg, Oscar
    KTH, School of Information and Communication Technology (ICT), Material Physics (Closed 20120101), Material Physics, MF (Closed 20120101).
    Story, T.
    Topological crystalline insulator states in Pb1-xSnxSe2012In: Nature Materials, ISSN 1476-1122, E-ISSN 1476-4660, Vol. 11, no 12, p. 1023-1027Article in journal (Refereed)
    Abstract [en]

    Topological insulators are a class of quantum materials in which time-reversal symmetry, relativistic effects and an inverted band structure result in the occurrence of electronic metallic states on the surfaces of insulating bulk crystals. These helical states exhibit a Dirac-like energy dispersion across the bulk bandgap, and they are topologically protected. Recent theoretical results have suggested the existence of topological crystalline insulators (TCIs), a class of topological insulators in which crystalline symmetry replaces the role of time-reversal symmetry in ensuring topological protection(1,2). In this study we show that the narrow-gap semiconductor Pb1-xSnxSe is a TCI for x = 0.23. Temperature-dependent angle-resolved photoelectron spectroscopy demonstrates that the material undergoes a temperature-driven topological phase transition from a trivial insulator to a TCI. These experimental findings add a new class to the family of topological insulators, and we anticipate that they will lead to a considerable body of further research as well as detailed studies of topological phase transitions.

  • 14. Edmonds, K. W.
    et al.
    Binns, C.
    Baker, S. H.
    Maher, M. J.
    Thornton, S. C.
    Tjernberg, Oscar
    KTH, Superseded Departments, Microelectronics and Information Technology, IMIT.
    Brookes, N. B.
    Magnetism of exposed and Co-capped Fe nanoparticles2000In: Journal of Magnetism and Magnetic Materials, ISSN 0304-8853, E-ISSN 1873-4766, Vol. 220, no 1, p. 25-30Article in journal (Refereed)
    Abstract [en]

    The effect of capping a dilute assembly of nanoscale mass-selected Fe clusters with a Co thin film has been studied using X-ray magnetic circular dichroism (XMCD). The clusters, containing around 400 atoms, were deposited in situ from a gas-aggregation source onto highly oriented pyrolytic graphite. The exposed clusters possess magnetic moments that are enhanced compared to the bulk, by around 4% for m(spin) and around 75% for m(orb). In addition, a surface core level shifted component is observed in the L-3.2 XMCD spectrum. Upon adding the Co layer, the surface component disappears, m(orb) is decreased for the Fe clusters, and m(spin) increases. The exposed clusters are magnetically isotropic but a strong in-plans anisotropy is observed after depositing the Co overlayer. We attribute this to the shape of the Co islands in which the Fe clusters are embedded.

  • 15. Edmonds, K. W.
    et al.
    Binns, C.
    Baker, S. H.
    Maher, M. J.
    Thornton, S. C.
    Tjernberg, Oscar
    KTH, Superseded Departments, Microelectronics and Information Technology, IMIT.
    Brookes, N. B.
    Size dependence of the magnetic moments of exposed nanoscale iron particles2001In: Journal of Magnetism and Magnetic Materials, ISSN 0304-8853, E-ISSN 1873-4766, Vol. 231, no 1, p. 113-119Article in journal (Refereed)
    Abstract [en]

    The magnetic moments in exposed, mass-selected, nanoscale Fe clusters in the size range 1.89-2.20 nm (300-475 atoms), deposited onto graphic in situ have been measured by X-ray magnetic circular dichroism. The smallest clusters possess moments that are enhanced by around 4% for m(spin) and 80% for m(orb) and decrease towards the bulk value with increasing size. The larger clusters show an in-plane anisotropy that is consistent with the anisotropy in the orbital moment. The smallest clusters are, within experimental error, magnetically isotropic. The anisotropy constant in the 475-atom clusters is significantly higher than the bulk value.

  • 16. Fatuzzo, C. G.
    et al.
    Sassa, Y.
    Månsson, Martin
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Material Physics, MF.
    Pailhes, S.
    Lipscombe, O. J.
    Hayden, S. M.
    Patthey, L.
    Shi, M.
    Grioni, M.
    Rønnow, H. M.
    Mesot, J.
    Tjernberg, Oscar
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Material Physics, MF.
    Chang, J.
    Nodal Landau Fermi-liquid quasiparticles in overdoped La1.77Sr0.23CuO42014In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 89, no 20, p. 205104-Article in journal (Refereed)
    Abstract [en]

    Nodal angle-resolved photoemission spectra taken on overdoped La1.77Sr0.23CuO4 are presented and analyzed. It is proven that the low-energy excitations are true Landau Fermi-liquid quasiparticles. We show that momentum and energy distribution curves can be analyzed self-consistently without quantitative knowledge of the bare band dispersion. Finally, by imposing Kramers-Kronig consistency on the self-energy Sigma, insight into the quasiparticle residue is gained. We conclude by comparing our results to quasiparticle properties extracted from thermodynamic, magnetoresistance, and high-field quantum oscillation experiments on overdoped Tl2Ba2CuO6+delta.

  • 17. Finazzi, M.
    et al.
    Ghiringhelli, G.
    Tjernberg, Oscar
    KTH, Superseded Departments, Microelectronics and Information Technology, IMIT.
    Brookes, N. B.
    Photon energy dependence of the perpendicular geometry magnetic circular dichroism in the 2p3p3p resonant photoemission from Ni2000In: Journal of Physics: Condensed Matter, ISSN 0953-8984, E-ISSN 1361-648X, Vol. 12, no 9, p. 2123-2133Article in journal (Refereed)
    Abstract [en]

    The magnetic circular dichroism in the perpendicular geometry of the resonant 2p3p3p photoemission (PE) spectroscopy has been investigated in metallic Ni as a function of the photon energy across the Ni Lj absorption edge. Within the experimental error bars, the photon energy dependence of the PE dichroism signal is the same as the one shown by the magnetic circular dichroism of the corresponding x-ray absorption (XMCD), obtained in the collinear geometry. This is attributed to the fact that, in metal Ni, the orbital [L-z] and dipolar [T-z] moments are smaller than the spin angular moment [S-z]. The latter is the dominating term in both the expressions that give the integrated values of the PE dichroism or XMCD intensities, Although the respective photon energy dependence is very similar, the normalized PE dichroism intensity is a factor similar to 5.6 smaller than the normalized XMCD signal, while only a factor similar to 1.6 is expected from theoretical considerations. This factor is observed even below the L-3 threshold, thus we exclude that the small intensity of the perpendicular geometry dichroism in the Ni 2p3p3p resonant photoemission is due to fast relaxation processes in the intermediate state.

  • 18. Finazzi, M.
    et al.
    Ghiringhelli, G.
    Tjernberg, Oscar
    KTH, Superseded Departments, Microelectronics and Information Technology, IMIT.
    Duo, L.
    Tagliaferri, A.
    Ohresser, P.
    Brookes, N. B.
    Multiatomic resonant photoemission spectroscopy on CuO and NiO: Observation of antiresonant behavior2000In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 62, no 24, p. R16215-R16218Article in journal (Refereed)
    Abstract [en]

    The intensity of the O 1s core photoemission peak has been measured for CuO and NiO as the photon energy is scanned across the L-3 absorption edge of the metal ion. In CuO, the O 1s peak shows a typical antiresonant behavior, with a sizable decrease of its cross section at photon energies below the Cu L-3 threshold. No detectable effect is observed for NiO. The CuO data are well reproduced by a multiatom resonant photoemission model based on resonant light scattering.

  • 19. Finazzi, M.
    et al.
    Ghiringhelli, G.
    Tjernberg, Oscar
    KTH, Superseded Departments, Microelectronics and Information Technology, IMIT.
    Ohresser, P.
    Brookes, N. B.
    Radiationless Raman versus Anger behavior at the Cu L-3 resonance of CuO and Cu2O2000In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 61, no 7, p. 4629-4635Article in journal (Refereed)
    Abstract [en]

    We have investigated the behavior of the 2p3p3p and 2p3s3p Anger lines of CuO and Cu2O scanning the photon energy across the Cu L-3 resonance. For both samples, when the excitation energy is below the L-3 resonance, we observe the 2p3p3p and 2p3s3p peaks at constant binding energy. This behavior is typical of nonradiative resonant Raman scattering. If the photon energy is raised above the L-3 maximum, the two samples behave in different ways. In CuO, the Auger peaks are always observed at constant binding energy, while in Cu2O their kinetic energy first reaches a maximum at correspondence with the absorption threshold, and then stabilizes at a value slightly higher than the off-resonance Auger peaks. These differences are interpreted in terms of the different electronic structure of the Auger intermediate state at resonance. In CuO, the intermediate state corresponds to a single 2p(3/2) core hole, with the Cu 3d band completely filled. On the contrary, in Cu2O the intermediate state is represented by the combination of a 2p(3/2) hole with a 4sp electron in strong interaction with the O-2sp valence band. In CuO, for photon energies higher than 1.5 eV above the L-3-edge maximum, the constant binding energy radiationless Raman peaks are accompanied by constant kinetic energy replicas. These are attributed to the relaxation of the Auger intermediate state through electron-hole pair generation across the band gap of the material. Satellites that could be associated to relaxation precesses involving energies smaller than the band gap are not resolved. No variation of the lineshape of the Anger peaks is observed as a function of the sample temperature, indicating that different densities of thermally accessible excitations do not have a strong influence on the recombination process of the core hole.

  • 20.
    Forslund, Ola Kenji
    et al.
    KTH, School of Engineering Sciences (SCI), Applied Physics, Materials and Nanophysics.
    Andreica, D.
    Sassa, Y.
    Nozaki, H.
    Umegaki, I.
    Nocerino, Elisabetta
    KTH, School of Engineering Sciences (SCI), Applied Physics, Materials and Nanophysics.
    Jonsson, Viktor
    KTH, School of Engineering Sciences (SCI), Applied Physics, Materials and Nanophysics.
    Tjernberg, Oscar
    KTH, School of Engineering Sciences (SCI), Applied Physics, Materials and Nanophysics.
    Guguchia, Z.
    Shermadini, Z.
    Khasanov, R.
    Isobe, M.
    Takagi, H.
    Ueda, Y.
    Sugiyama, J.
    Månsson, Martin
    KTH, School of Engineering Sciences (SCI), Applied Physics, Materials and Nanophysics.
    Magnetic phase diagram of K 2 Cr 8 O 16 clarified by high-pressure muon spin spectroscopy2019In: Scientific Reports, ISSN 2045-2322, E-ISSN 2045-2322, Vol. 9, no 1, article id 1141Article in journal (Refereed)
    Abstract [en]

    The K 2 Cr 8 O 16 compound belongs to a series of quasi-1D compounds with intriguing magnetic properties that are stabilized through a high-pressure synthesis technique. In this study, a muon spin rotation, relaxation and resonance (μ + SR) technique is used to investigate the pressure dependent magnetic properties up to 25 kbar. μ + SR allows for measurements in true zero applied field and hereby access the true intrinsic material properties. As a result, a refined temperature/pressure phase diagram is presented revealing a novel low temperature/high pressure (p C1 = 21 kbar) transition from a ferromagnetic insulating to a high-pressure antiferromagnetic insulator. Finally, the current study also indicates the possible presence of a quantum critical point at p C2 ~ 33 kbar where the magnetic order in K 2 Cr 8 O 16 is expected to be fully suppressed even at T = 0 K.

  • 21. Ghiringhelli, G.
    et al.
    Brookes, N. B.
    Tjeng, L. H.
    Mizokawa, T.
    Tjernberg, Oscar
    KTH, Superseded Departments, Microelectronics and Information Technology, IMIT.
    Steeneken, P. G.
    Menovsky, A. A.
    Probing the singlet character of the two-hole states in cuprate superconductors2002In: Physica. B, Condensed matter, ISSN 0921-4526, E-ISSN 1873-2135, Vol. 312, p. 34-35Article in journal (Refereed)
    Abstract [en]

    Using spin-resolved resonant photoemission we have probed the singlet vs. triplet character of the two-hole state in the layered cuprates Bi2Sr2CaCu2O8+delta La2-xSrxCuO4 and Sr2CuO2Cl2. The combination of the photon circular polarization with the photoelectron spin detection gives access to the character of the photoemission final states, which correspond to the two-hole configurations localized at a (CuO4) site. In particular, the lowest energy state is found to have a very high singlet character in all the measured compounds. This can be considered as a strong indication of the existence and stability of the so-called Zhang-Rice singlets in the layered cuprates.

  • 22. Ghiringhelli, G.
    et al.
    Tjeng, L. H.
    Tanaka, A.
    Tjernberg, Oscar
    KTH, Superseded Departments, Microelectronics and Information Technology, IMIT.
    Mizokawa, T.
    de Boer, J. L.
    Brookes, N. B.
    3d spin-orbit photoemission spectrum of nonferromagnetic materials: The test cases of CoO and Cu2002In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 66, no 7Article in journal (Refereed)
    Abstract [en]

    The x-ray photoemission spectrum of the valence states of 3d transition-metal systems is spin polarized when using circularly polarized photons. The integral of the spin-orbit spectrum is proportional to the expectation value of the angular part of the 3d spin-orbit operator in the initial state. We show that this quantity can be used to get an estimate of the atomic orbital moment. While the measurement is sensitive to the magnetization axis, it does not require a net macroscopic magnetization nor the presence of a long-range magnetic order, and is therefore suitable for any transition-metal systems being antiferromagnetic or paramagnetic or magnetically disordered. In the case of full 3d shell the integral of the spin-orbit spectrum is zero, but the spectral shape can give a direct estimate of the 3d spin-orbit energy splitting DeltaE(SO). We have used Cu and CoO to experimentally test this technique. As expected Cu provides a vanishing result for , whereas for Co2+ in CoO we find =1.36h at 0 K. On the other hand we find DeltaE(SO)similar or equal to280 meV for Cu.

  • 23.
    Grishin, Michael A.
    et al.
    KTH, Superseded Departments, Microelectronics and Information Technology, IMIT.
    Månsson, Martin
    KTH, Superseded Departments, Microelectronics and Information Technology, IMIT.
    Tjernberg, Oscar
    KTH, Superseded Departments, Microelectronics and Information Technology, IMIT.
    Claesson, Thomas
    KTH, Superseded Departments, Microelectronics and Information Technology, IMIT.
    Karlsson, Henrik S.
    Optillion AB.
    Karlsson, Ulf O.
    KTH, Superseded Departments, Microelectronics and Information Technology, IMIT.
    A bandgap surface state at the GaSb(001) surface observed by femtosecond laser pump-and-probe photoemission spectroscopyManuscript (Other academic)
  • 24.
    Grishin, Michael A.
    et al.
    KTH, Superseded Departments, Microelectronics and Information Technology, IMIT.
    Månsson, Martin
    KTH, Superseded Departments, Microelectronics and Information Technology, IMIT.
    Tjernberg, Oscar
    KTH, Superseded Departments, Microelectronics and Information Technology, IMIT.
    Karlsson, Henrik S.
    Optillion AB.
    Karlsson, Ulf O.
    KTH, Superseded Departments, Microelectronics and Information Technology, IMIT.
    A new two-dimensional angle-resolving multi-anode electron detector for femtosecond photoemission spectroscopyArticle in journal (Other academic)
  • 25.
    Grishin, Michael A.
    et al.
    KTH, School of Information and Communication Technology (ICT), Material Physics.
    Månsson, Martin
    KTH, School of Information and Communication Technology (ICT), Microelectronics and Applied Physics, MAP.
    Tjernberg, Oscar
    KTH, School of Information and Communication Technology (ICT), Material Physics.
    Karlsson, Henrik S.
    Optillion AB, Stockholm.
    Karlsson, Ulf O.
    KTH, School of Information and Communication Technology (ICT), Material Physics.
    Anisotropy of electron structure at InAs(111) surfaces by laser pump-and-probe photoemission spectroscopy2005In: Surface Science, ISSN 0039-6028, E-ISSN 1879-2758, Vol. 574, no 1, p. 89-94Article in journal (Refereed)
    Abstract [en]

    The electronic structure and the electron dynamics of the clean InAs(111)A 2 x 2 and the InAs(111)B 1 x 1 surfaces have been studied by laser pump-and-probe photoemission spectroscopy. Normally unpopulated electron states above the valence band maximum (VBM) are filled on the InAs(111)A surface due to the conduction band pinning above the Fermi level (E-F). Accompanied by the downward band banding alignment, a charge accumulation layer is confined to the surface region creating a two dimensional electron gas (2DEG). The decay of the photoexcited carriers above the conduction band minimum (CBM) is originated by bulk states affected by the presence of the surface. No occupied states were found on the InAs(111)B 1 x 1 surface. This fact is suggested to be due to the surface stabilisation by the charge removal from the surface into the bulk. The weak photoemission intensity above the VBM on the (111)B surface is attributed to electron states trapped by surface defects. The fast decay of the photoexcited electron states on the (111)A and the (111)B surfaces was found to be tau(111A) less than or equal to 5 ps and tau(111B) less than or equal to 4ps, respectively. We suggest the diffusion of the hot electrons into the bulk is the decay mechanism. (

  • 26.
    Horio, M.
    et al.
    Univ Zurich, Phys Inst, Winterthurerstr 190, CH-8057 Zurich, Switzerland..
    Hauser, K.
    Univ Zurich, Phys Inst, Winterthurerstr 190, CH-8057 Zurich, Switzerland..
    Sassa, Y.
    Uppsala Univ, Dept Phys & Astron, SE-75121 Uppsala, Sweden..
    Mingazheva, Z.
    Univ Zurich, Phys Inst, Winterthurerstr 190, CH-8057 Zurich, Switzerland..
    Sutter, D.
    Univ Zurich, Phys Inst, Winterthurerstr 190, CH-8057 Zurich, Switzerland..
    Kramer, K.
    Univ Zurich, Phys Inst, Winterthurerstr 190, CH-8057 Zurich, Switzerland..
    Cook, A.
    Univ Zurich, Phys Inst, Winterthurerstr 190, CH-8057 Zurich, Switzerland..
    Nocerino, Elisabetta
    KTH, School of Engineering Sciences (SCI), Applied Physics, Materials and Nanophysics.
    Forslund, Ola Kenji
    KTH, School of Engineering Sciences (SCI), Applied Physics, Materials and Nanophysics.
    Tjernberg, Oscar
    KTH, Centres, Nordic Institute for Theoretical Physics NORDITA. KTH, School of Engineering Sciences (SCI), Applied Physics, Materials and Nanophysics.
    Kobayashi, M.
    Paul Scherrer Inst, Swiss Light Source, CH-5232 Villigen, Switzerland..
    Chikina, A.
    Paul Scherrer Inst, Swiss Light Source, CH-5232 Villigen, Switzerland..
    Schroter, N. B. M.
    Paul Scherrer Inst, Swiss Light Source, CH-5232 Villigen, Switzerland..
    Krieger, J. A.
    Paul Scherrer Inst, Lab Muon Spin Spect, CH-5232 Villigen, Switzerland.;Swiss Fed Inst Technol, Lab Festkorperphys, CH-8093 Zurich, Switzerland..
    Schmitt, T.
    Paul Scherrer Inst, Swiss Light Source, CH-5232 Villigen, Switzerland..
    Strocov, V. N.
    Paul Scherrer Inst, Swiss Light Source, CH-5232 Villigen, Switzerland..
    Pyon, S.
    Univ Tokyo, Dept Adv Mat, Kashiwa, Chiba 2778561, Japan..
    Takayama, T.
    Univ Tokyo, Dept Adv Mat, Kashiwa, Chiba 2778561, Japan..
    Takagi, H.
    Univ Tokyo, Dept Adv Mat, Kashiwa, Chiba 2778561, Japan..
    Lipscombe, O. J.
    Univ Bristol, HH Wills Phys Lab, Bristol BS8 1TL, Avon, England..
    Hayden, S. M.
    Univ Bristol, HH Wills Phys Lab, Bristol BS8 1TL, Avon, England..
    Ishikado, M.
    CROSS, Tokai, Ibaraki 3191106, Japan..
    Eisaki, H.
    Natl Inst Adv Ind Sci & Technol, Elect & Photon Res Inst, Tsukuba 3058568, Japan..
    Neupert, T.
    Univ Zurich, Phys Inst, Winterthurerstr 190, CH-8057 Zurich, Switzerland..
    Månsson, Martin
    KTH, School of Engineering Sciences (SCI), Applied Physics, Materials and Nanophysics.
    Matt, C. E.
    Univ Zurich, Phys Inst, Winterthurerstr 190, CH-8057 Zurich, Switzerland.;Paul Scherrer Inst, Swiss Light Source, CH-5232 Villigen, Switzerland.;Harvard Univ, Dept Phys, Cambridge, MA 02138 USA..
    Chang, J.
    Univ Zurich, Phys Inst, Winterthurerstr 190, CH-8057 Zurich, Switzerland..
    Three-Dimensional Fermi Surface of Overdoped La-Based Cuprates2018In: Physical Review Letters, ISSN 0031-9007, E-ISSN 1079-7114, Vol. 121, no 7, article id 077004Article in journal (Refereed)
    Abstract [en]

    We present a soft x-ray angle-resolved photoemission spectroscopy study of overdoped high-temperature superconductors. In-plane and out-of-plane components of the Fermi surface are mapped by varying the photoemission angle and the incident photon energy. No k(z) dispersion is observed along the nodal direction, whereas a significant antinodal k(z) dispersion is identified for La-based cuprates. Based on a tight-binding parametrization, we discuss the implications for the density of states near the van Hove singularity. Our results suggest that the large electronic specific heat found in overdoped La2-xSrxCuO4 cannot be assigned to the van Hove singularity alone. We therefore propose quantum criticality induced by a collapsing pseudogap phase as a plausible explanation for observed enhancement of electronic specific heat.

  • 27.
    Hårdensson Berntsen, Magnus
    et al.
    KTH, School of Engineering Sciences (SCI), Applied Physics, Materials and Nanophysics.
    Götberg, Olof
    KTH, School of Engineering Sciences (SCI), Applied Physics, Materials and Nanophysics.
    Tjernberg, Oscar
    KTH, School of Engineering Sciences (SCI), Applied Physics, Materials and Nanophysics.
    Reinvestigation of the giant Rashba-split states on Bi-covered Si(111)2018In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 97, no 12, article id 125148Article in journal (Refereed)
    Abstract [en]

    We study the electronic and spin structures of the giant Rashba-split surface states of the Bi/Si(111)-(root 3 x root 3)R30 degrees trimer phase by means of spin- and angle-resolved photoelectron spectroscopy (spin-ARPES). Supported by tight-binding calculations of the surface state dispersion and spin orientation, our findings show that the spin experiences a vortexlike structure around the (Gamma) over bar point of the surface Brillouin zone-in accordance with the standard Rashba model. Moreover, we find no evidence of a spin vortex around the (K) over bar point in the hexagonal Brillouin zone and thus no peculiar Rashba split around this point, something that has been suggested by previous works. Rather the opposite, our results show that the spin structure around (K) over bar can be fully understood by taking into account the symmetry of the Brillouin zone and the intersection of spin vortices centered around the (Gamma) over bar points in neighboring Brillouin zones. As a result, the spin structure is consistently explained within the standard framework of the Rashba model although the spin-polarized surface states experience a more complex dispersion compared to free-electron-like parabolic states.

  • 28. Janin, E.
    et al.
    von Schenck, H.
    Hellden, S.
    Tjernberg, Oscar
    KTH, Superseded Departments, Microelectronics and Information Technology, IMIT.
    Karlsson, Ulf O.
    KTH, Superseded Departments, Microelectronics and Information Technology, IMIT.
    Göthelid, Mats
    KTH, Superseded Departments, Microelectronics and Information Technology, IMIT.
    Corrosive adsorption of Sn on the Pt(110)(1 x 2) surface2002In: Surface Science, ISSN 0039-6028, E-ISSN 1879-2758, Vol. 515, no 03-feb, p. 462-470Article in journal (Refereed)
    Abstract [en]

    Room temperature deposition of Sn on the Pt(110)(1 x 2) surface has been studied by scanning tunnelling microscopy and core level photoelectron spectroscopy. At low coverage Sri is found in three different configurations; as mobile adatoms in the valley of the missing-row reconstruction, as 1D-Pt-Sn-Pt- alloy chains forming local Pt3Sn(110)2 x 2 regions and finally as 3D alloy islands. At higher coverage these islands form a platinum rich alloy film, which is dissolved in the crystal upon annealing to 600 degreesC.

  • 29. Koethe, T. C.
    et al.
    Hu, Z.
    Haverkort, M. W.
    Schuessler-Langeheine, C.
    Venturini, F.
    Brookes, N. B.
    Tjernberg, Oscar
    KTH, School of Information and Communication Technology (ICT), Material Physics, Material Physics, MF.
    Reichelt, W.
    Hsieh, H. H.
    Lin, H. J.
    Chen, C. T.
    Tjeng, L. H.
    Transfer of spectral weight and symmetry across the metal-insulator transition in VO22006In: Physical Review Letters, ISSN 0031-9007, E-ISSN 1079-7114, Vol. 97, no 11Article in journal (Refereed)
    Abstract [en]

    We present a detailed study of the valence and conduction bands of VO2 across the metal-insulator transition using bulk-sensitive photoelectron and O K x-ray absorption spectroscopies. We observe a giant transfer of spectral weight with distinct features that require an explanation which goes beyond the Peierls transition model as well as the standard single-band Hubbard model. Analysis of the symmetry and energies of the bands reveals the decisive role of the V 3d orbital degrees of freedom. Comparison to recent realistic many body calculations shows that much of the k dependence of the self-energy correction can be cast within a dimer model.

  • 30. Mansson, M.
    et al.
    Claesson, T.
    Finazzi, M.
    Dallera, C.
    Brookes, N. B.
    Tjernberg, Oscar
    KTH, School of Information and Communication Technology (ICT), Microelectronics and Information Technology, IMIT.
    Using High Energy Angle Resolved Photoelectron Spectroscopy to Reveal the Charge Density in Solids2008In: Physical Review Letters, ISSN 0031-9007, E-ISSN 1079-7114, Vol. 101, no 22Article in journal (Refereed)
    Abstract [en]

    The charge density in solids is a fundamental parameter. Here we demonstrate that the charge density can be determined by the use of angle resolved photoelectron spectroscopy. The method, which involves a Fourier-like transform from momentum space to real space, is demonstrated by utilizing soft x-ray angle resolved photoelectron spectroscopy to sample the complete three-dimensional Brillouin zone of copper. It is also shown that this can be done in an energy resolved way as to extract the charge density contribution from states of a particular energy.

  • 31. Matt, C. E.
    et al.
    Fatuzzo, C. G.
    Sassa, Y.
    Mansson, M.
    Fatale, S.
    Bitetta, V.
    Shi, X.
    Pailhes, S.
    Hårdensson Berntsen, Magnus
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Material Physics, MF.
    Kurosawa, T.
    Oda, M.
    Momono, N.
    Lipscombe, O. J.
    Hayden, S. M.
    Yan, J. -Q
    Zhou, J. -S
    Goodenough, J. B.
    Pyon, S.
    Takayama, T.
    Takagi, H.
    Patthey, L.
    Bendounan, A.
    Razzoli, E.
    Shi, M.
    Plumb, N. C.
    Radovic, M.
    Grioni, M.
    Mesot, J.
    Tjernberg, Oscar
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Material Physics, MF. Stockholm University, Sweden.
    Chang, J.
    Electron scattering, charge order, and pseudogap physics in La1.6-xNd0.4SrxCuO4: An angle-resolved photoemission spectroscopy study2015In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 92, no 13, article id 134524Article in journal (Refereed)
    Abstract [en]

    We report an angle-resolved photoemission study of the charge stripe ordered La1.6-xNd0.4SrxCuO4 (Nd-LSCO) system. A comparative and quantitative line-shape analysis is presented as the system evolves from the overdoped regime into the charge ordered phase. On the overdoped side (x = 0.20), a normal-state antinodal spectral gap opens upon cooling below 80 K. In this process, spectral weight is preserved but redistributed to larger energies. A correlation between this spectral gap and electron scattering is found. A different line shape is observed in the antinodal region of charge ordered Nd-LSCO x = 1/8. Significant low-energy spectral weight appears to be lost. These observations are discussed in terms of spectral-weight redistribution and gapping originating from charge stripe ordering.

  • 32. Matt, C. E.
    et al.
    Sutter, D.
    Cook, A. M.
    Sassa, Y.
    Månsson, Martin
    KTH, School of Engineering Sciences (SCI), Applied Physics, Material Physics, MF.
    Tjernberg, Oscar
    KTH, School of Engineering Sciences (SCI), Applied Physics, Material Physics, MF.
    Das, L.
    Horio, M.
    Destraz, D.
    Fatuzzo, C. G.
    Hauser, K.
    Shi, M.
    Kobayashi, M.
    Strocov, V. N.
    Schmitt, T.
    Dudin, P.
    Hoesch, M.
    Pyon, S.
    Takayama, T.
    Takagi, H.
    Lipscombe, O. J.
    Hayden, S. M.
    Kurosawa, T.
    Momono, N.
    Oda, M.
    Neupert, T.
    Chang, J.
    Direct observation of orbital hybridisation in a cuprate superconductor2018In: Nature Communications, ISSN 2041-1723, E-ISSN 2041-1723, Vol. 9, article id 972Article in journal (Refereed)
    Abstract [en]

    The minimal ingredients to explain the essential physics of layered copper-oxide (cuprates) materials remains heavily debated. Effective low-energy single-band models of the copper-oxygen orbitals are widely used because there exists no strong experimental evidence supporting multi-band structures. Here, we report angle-resolved photoelectron spectroscopy experiments on La-based cuprates that provide direct observation of a two-band structure. This electronic structure, qualitatively consistent with density functional theory, is parametrised by a two-orbital (d(x2-y2) and d(z2)) tight-binding model. We quantify the orbital hybridisation which provides an explanation for the Fermi surface topology and the proximity of the van-Hove singularity to the Fermi level. Our analysis leads to a unification of electronic hopping parameters for single-layer cuprates and we conclude that hybridisation, restraining d-wave pairing, is an important optimisation element for superconductivity.

  • 33. Medarde, M.
    et al.
    Dallera, C.
    Grioni, M.
    Voigt, J.
    Podlesnyak, A.
    Pomjakushina, E.
    Conder, K.
    Neisius, T.
    Tjernberg, Oscar
    KTH, School of Information and Communication Technology (ICT), Microelectronics and Information Technology, IMIT.
    Barilo, S. N.
    Low-temperature spin-state transition in LaCoO3 investigated using resonant x-ray absorption at the CoK edge2006In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 73, no 5Article in journal (Refereed)
    Abstract [en]

    LaCoO3 displays two broad anomalies in the DC magnetic susceptibility chi(DC), occurring, respectively, around 50 K and 500 K. We have investigated the first of them within the 10 K < T < RT temperature range using Co K alpha(1) x-ray absorption spectroscopy (XAS) in the partial fluorescence yield mode. In contrast with previous O K-edge XAS reports, our data show the existence of abrupt changes around 50 K which can be nicely correlated with the anomaly in chi(DC). To our knowledge, this is the first time that a clear, quantitative relationship between the temperature dependence of the magnetic susceptibility and that of the XAS spectra is reported. The intensity changes in the preedge region, which are consistent with a transition from a lower to a higher spin state, have been analyzed using a minimal model including the Co 3d and O 2p hybridization in the initial state. The temperature dependence of the Co magnetic moment obtained from the estimated e(g) and t(2g) occupations could be satisfactorily reproduced. Also, the decrease of the Co 3d and O 2p hybridization by increasing temperature obtained from this simple model compares favorably with the values estimated from thermal evolution of the crystallographic structure.

  • 34. Minar, J.
    et al.
    Ebert, H.
    Ghiringhelli, G.
    Tjernberg, Oscar
    KTH, Superseded Departments, Microelectronics and Information Technology, IMIT.
    Brookes, N. B.
    Tjeng, L. H.
    Theoretical description of the Fano effect in the angle-integrated valence-band photoemission of paramagnetic solids2001In: Physical Review B Condensed Matter, ISSN 0163-1829, E-ISSN 1095-3795, Vol. 6314, no 14Article in journal (Refereed)
    Abstract [en]

    A theoretical description of the Fano effect in the angle-integrated valence-band photoemission of paramagnetic solids is presented that is based on the one-step model of photoemission and relativistic multiple-scattering theory. Applications to fcc-Cu led to a very satisfying agreement with recent experimental data that show the Fano effect, i.e., a finite spin-polarization for the spectra is found for excitation with circularly polarized radiation. As can be demonstrated by model calculations. this finding is caused by the presence of spin-orbit coupling. To allow for a more detailed discussion of the spectra a simplified description of the Fano effect is presented that treats spin-orbit coupling as a perturbation.

  • 35. Minar, J.
    et al.
    Ebert, H.
    Tjeng, L. H.
    Steeneken, P.
    Ghiringhelli, G.
    Tjernberg, Oscar
    KTH, Superseded Departments, Microelectronics and Information Technology, IMIT.
    Brookess, N. B.
    Theoretical description of the Fano-effect in the angle-integrated valence-band photoemission of paramagnetic solids2001In: Applied Physics A: Materials Science & Processing, ISSN 0947-8396, E-ISSN 1432-0630, Vol. 73, no 6, p. 663-666Article in journal (Refereed)
    Abstract [en]

    A theoretical description of the Fano-effect in the angle-integrated valence-band photoemission (VB XPS) of paramagnetic solids is presented that is based on the one-step model of photoemission and relativistic multiple scattering theory. Applications to fcc-Cu and fcc-Ag led to a very satisfying agreement with recent experimental data that show the Fano-effect, i.e., a finite spin polarisation of the photoelectrons is found for excitation with circularly polarised radiation. As can be demonstrated by model calculations, this finding is caused by the presence of spin-orbit coupling. To allow for a more detailed discussion of the spectra, a simplified description of the Fano-effect is presented that treats spin-orbit coupling as a perturbation.

  • 36. Mizokawa, T.
    et al.
    Tjeng, L. H.
    Sawatzky, G. A.
    Ghiringhelli, G.
    Tjernberg, Oscar
    KTH, Superseded Departments, Microelectronics and Information Technology, IMIT.
    Brookes, N. B.
    Fukazawa, H.
    Nakatsuji, S.
    Maeno, Y.
    Spin-orbit coupling in the Mott insulator Ca2RuO42001In: Physical Review Letters, ISSN 0031-9007, E-ISSN 1079-7114, Vol. 8707, no 7Article in journal (Refereed)
    Abstract [en]

    O 1s x-ray absorption study of the Mott insulator Ca2RuO4 shows that the orbital population of the 4d t(2g) band dramatically changes with temperature. In addition, spin-resolved circularly polarized photoemission study of Ca2RuO4 shows that a substantial orbital angular momentum is induced in the Ru 4d t(2g) band. Based on the experimental results and model Hartree-Fock calculations, we argue that the cooperation between the strong spin-orbit coupling in the Ru 4d t(2g) band and the small distortion of the RuO6 octahedra causes the interesting changeover of the spin and orbital anisotropy as a function of temperature.

  • 37. Månsson, M.
    et al.
    Pra, K.
    Sassa, Y.
    Tobash, P. H.
    Bauer, E. D.
    Rusu, C.
    Andreica, D.
    Tjernberg, Oscar
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Material Physics, MF.
    Sedlak, K.
    Grioni, M.
    Durakiewicz, T.
    Sugiyama, J.
    Magnetic order in the 2D Heavy-Fermion system CePt2In7 studied by μ+SR2014In: 13TH INTERNATIONAL CONFERENCE ON MUON SPIN ROTATION, RELAXATION AND RESONANCE, 2014, Vol. 551, no 1, p. 012028-, article id 012028Conference paper (Refereed)
    Abstract [en]

    The low-temperature microscopic magnetic properties of the quasi-2D heavy- fermion compound, CePt2In7 are investigated by using a positive muon-spin rotation and relaxation (μ+SR) technique. Clear evidence for the formation of a commensurate antiferromagnetic order below TN 5.40 K is presented. The magnetic order parameter is shown to fit well to a modified BCS gap-energy function in a strong-coupling scenario.

  • 38.
    Månsson, Martin
    et al.
    KTH, School of Information and Communication Technology (ICT), Microelectronics and Applied Physics, MAP.
    Claesson, Thomas
    KTH, School of Information and Communication Technology (ICT).
    Finazzi, Marco
    Dallera, Claudia
    De Nadaï, Celine
    Brookes, Nicholas B.
    Tjernberg, Oscar
    KTH, School of Information and Communication Technology (ICT).
    Revealing the charge density in solidsManuscript (Other academic)
  • 39.
    Månsson, Martin
    et al.
    KTH, School of Information and Communication Technology (ICT), Microelectronics and Applied Physics, MAP.
    Claesson, Thomas
    KTH, School of Information and Communication Technology (ICT).
    Hayden, S. M.
    Tjernberg, Oscar
    KTH, School of Information and Communication Technology (ICT).
    Chang, Johan
    Pailhés, Stephane
    Shi, Ming
    Mesot, Joël
    Patthey, Luc
    Momono, Naoki
    Oda, Migaku
    Ido, Masayuki
    Experimental evidence of a quantum phase transition in La(2-x)Sr(x)CuO4()Manuscript (Other academic)
  • 40.
    Månsson, Martin
    et al.
    KTH, School of Information and Communication Technology (ICT), Material Physics.
    Claesson, Thomas
    KTH, School of Information and Communication Technology (ICT), Material Physics.
    Karlsson, Ulf O.
    KTH, School of Information and Communication Technology (ICT), Material Physics.
    Tjernberg, Oscar
    KTH, School of Information and Communication Technology (ICT), Material Physics.
    Pailhés, Stephane
    Laboratory for Neutron Scattering, ETH Zürich.
    Chang, Johan
    Laboratory for Neutron Scattering, ETH Zürich.
    Mesot, Joël
    Laboratory for Neutron Scattering, ETH Zürich.
    Shi, Ming
    Swiss Light Source, Paul Scherrer Institut, Villigen.
    Patthey, Luc
    Swiss Light Source, Paul Scherrer Institut, Villigen.
    Momono, Naoki
    Department of Physics, Hokkaido University, Sapporo.
    Oda, Migaku
    Department of Physics, Hokkaido University, Sapporo.
    Ido, Masayuki
    Department of Physics, Hokkaido University, Sapporo.
    On-board sample cleaver2007In: Review of Scientific Instruments, ISSN 0034-6748, E-ISSN 1089-7623, Vol. 78, no 7, p. 076103-Article in journal (Refereed)
    Abstract [en]

    An on-board sample cleaver has been developed in order to cleave small and hard-to-cleave samples. To acquire good cleaves from rigid samples the alignment of the cleaving blade with respect to the internal crystallographic planes is crucial. To have the opportunity to mount the sample and align it to the blade ex situ has many advantages. The design presented has allowed us to cleave very tiny and rigid samples, e.g., the high-temperature superconductor La(2-x)SrxCuO4. Further, in this design the sample and the cleaver will have the same temperature, allowing us to cleave and keep the sample at low temperature. This is a big advantage over prior cleaver systems. As a result, better surfaces and alignments can be realized, which considerably simplifies and improves the experiments.

  • 41.
    Månsson, Martin
    et al.
    KTH, School of Information and Communication Technology (ICT), Microelectronics and Applied Physics, MAP.
    Grishin, Michael A.
    KTH, School of Information and Communication Technology (ICT), Material Physics (Closed 20120101).
    Tjernberg, Oscar
    KTH, School of Information and Communication Technology (ICT), Material Physics (Closed 20120101).
    Claesson, Thomas
    KTH, School of Information and Communication Technology (ICT), Material Physics (Closed 20120101).
    Karlsson, Henrik S.
    KTH, School of Information and Communication Technology (ICT), Material Physics (Closed 20120101).
    Karlsson, Ulf O.
    KTH, School of Information and Communication Technology (ICT), Material Physics (Closed 20120101).
    Electronic structure and electron dynamics at the GaSb(001) surface studied by femtosecond pump-and-probe pulsed laser photoemission spectroscopy2006In: Applied Surface Science, ISSN 0169-4332, E-ISSN 1873-5584, Vol. 252, no 15, p. 5308-5311Article in journal (Refereed)
    Abstract [en]

    Transiently excited electron states at the GaSb(001) surface have been studied by means of time- and angle-resolved photoemission spectroscopy based on a femtosecond laser system. A normally unpopulated surface electron state has been found at similar to 250 meV above the valence band maximum with a strong confinement at the center of the surface Brillouin zone. The lifetime of transiently excited carriers at the intergap surface states has been found to be similar to 11 ps, associated with rapid carrier diffusion.

  • 42.
    Månsson, Martin
    et al.
    KTH, School of Information and Communication Technology (ICT), Microelectronics and Applied Physics, MAP.
    Tjernberg, Oscar
    KTH, School of Information and Communication Technology (ICT), Microelectronics and Applied Physics, MAP.
    Göthelid, Mats
    KTH, School of Information and Communication Technology (ICT), Microelectronics and Applied Physics, MAP.
    Grishin, Michael A.
    KTH, School of Information and Communication Technology (ICT), Microelectronics and Applied Physics, MAP.
    Claesson, Thomas
    KTH, School of Information and Communication Technology (ICT), Microelectronics and Applied Physics, MAP.
    Karlsson, Ulf O.
    KTH, School of Information and Communication Technology (ICT), Microelectronics and Applied Physics, MAP.
    Ultrafast electron dynamics and recombination at the Ge(111): Sn(root 3 X root 3)R30 degrees surface2008In: Surface Science Letters, ISSN 0039-6028, Vol. 602, no 5, p. L33-L37Article in journal (Refereed)
    Abstract [en]

    We present the first study revealing the electronic structure and electron dynamics of the excited adatom state at the Ge(111): Sn(root 3 x root 3)R30 degrees surface. By the use of time- and angle-resolved photoemission spectroscopy, the normally unoccupied electronic structure of the partly empty Sn adatom can be probed. From the angle-resolved data we conclude that the adatom electrons at the Ge:Sn surface are more delocalized than at the clean Ge(111)c(2 x 8) surface. A unique pump-and-probe technique, based on a pulsed femtosecond laser-system, has also allowed us to study the recombination process of the excited state. We connect the recombination process of the excited electrons to the coherent fluctuations of the Sn adatoms. As a result we present an estimate for the time between each collective and coherent adatom flip Delta t = 9 ps, i.e. an adatom switching frequency nu(SW) approximate to 0.1 THz. We find that our results, contrary to scanning tunneling microscopy measurements [F. Ronci, S. Colonna, S.D. Thorpe, A. Cricenti, G. Le Lay, Phys. Rev. Lett. 95 (2005) 156101], agree very well with values extracted from molecular dynamics simulations found in the literature [J. Avila, A. Mascaraque, E.G. Michel, M.C. Asensio, G. Le Lay, J. Ortega, R. Perez, F. Flores, Phys. Rev. Lett. 82 (1999) 442; D. Farias, W. Kaminski, J. Lobo, J. Ortega, E. Hulpke, R. Perez, F. Flores, E.G. Michel, Phys. Rev. Lett. 91 (2003) 16103].

  • 43.
    Månsson, Martin
    et al.
    KTH, School of Information and Communication Technology (ICT), Microelectronics and Applied Physics, MAP.
    Tjernberg, Oscar
    KTH, School of Information and Communication Technology (ICT), Microelectronics and Applied Physics, MAP.
    Göthelid, Mats
    KTH, School of Information and Communication Technology (ICT), Microelectronics and Applied Physics, MAP.
    Grishin, Michael A.
    KTH, School of Information and Communication Technology (ICT), Microelectronics and Applied Physics, MAP.
    Karlsson, Henrik S.
    KTH, School of Information and Communication Technology (ICT), Microelectronics and Applied Physics, MAP.
    Le Lay, Guy
    KTH, School of Information and Communication Technology (ICT), Microelectronics and Applied Physics, MAP.
    Claesson, Thomas
    KTH, School of Information and Communication Technology (ICT), Microelectronics and Applied Physics, MAP.
    Karlsson, Ulf O.
    KTH, School of Information and Communication Technology (ICT), Microelectronics and Applied Physics, MAP.
    Electronic structure and electron dynamics of delocalized adatom states at the Ge(111)c(2 x 8) surfaceIn: Physical Review B, ISSN 1098-0121Article in journal (Refereed)
  • 44. Ohresser, P.
    et al.
    Ghiringhelli, G.
    Tjernberg, Oscar
    KTH, Superseded Departments, Microelectronics and Information Technology, IMIT.
    Brookes, N. B.
    Finazzi, M.
    Magnetism of nanostructures studied by x-ray magnetic circular dichroism: Fe on Cu(111)2000In: Physical Review B Condensed Matter, ISSN 0163-1829, E-ISSN 1095-3795, Vol. 62, no 9, p. 5803-5809Article in journal (Refereed)
    Abstract [en]

    Epitaxial growth of Fe on a stepped Cu(111) surface leads to the formation of fee Fe stripes along the step edges for coverages lower than 1.5 monolayer (ML). Using the sensitivity of the x-ray magnetic circular dichroism and sum-rule analysis, the changes in the magnetic properties in the low thickness range from similar to 5% of a monolayer to 4 ML, covering the one-dimensional (1D) coalescence (similar to 0.8 ML) and the 2D percolation limit (similar to 1.5 ML), have been determined. The determination of the spin moment (m(spin)) indicates significant features which can be correlated to the morphological transition. In particular, the m(spin) decreases at the 1D coalescence limit, but increases as the film reaches the 2D percolation limit and starts to transform into the bcc phase. This behavior is tentatively ascribed to the decrease in the Fe atomic volume, as it is well known that such changes can dramatically modify the magnetic properties of gamma-Fe.

  • 45.
    Palmgren, Pål
    et al.
    KTH, School of Information and Communication Technology (ICT), Material Physics.
    Claesson, Thomas
    KTH, School of Information and Communication Technology (ICT), Material Physics.
    Önsten, Anneli
    KTH, School of Information and Communication Technology (ICT), Material Physics.
    Agnarsson, Björn
    KTH, School of Information and Communication Technology (ICT), Material Physics.
    Månsson, Martin
    KTH, School of Information and Communication Technology (ICT), Material Physics.
    Tjernberg, Oscar
    KTH, School of Information and Communication Technology (ICT), Material Physics.
    Göthelid, Mats
    KTH, School of Information and Communication Technology (ICT), Material Physics.
    Band bending and structure dependent HOMO energy at the ZnO(0001)-titanyl phthalocyanine interface2007In: Surface Science, ISSN 0039-6028, E-ISSN 1879-2758, Vol. 601, no 18, p. 4222-4226Article in journal (Refereed)
    Abstract [en]

    We have investigated the initial stages of titanyl phthalocyanine (TiOPc) growth on single crystalline ZnO(0 0 0 1). This organic-semiconductor interface is self-organizing as a 2 x 1 pattern appears in a low energy electron diffraction upon deposition of the molecules. To achieve this pattern, the TiOPc is suggested to adsorb standing with the edge of the molecule along the substrate atomic rows. Photoelectron spectroscopy is used to further analyze the interface; a relatively large upwards band bending amounting to 0.5 eV is found and a splitting of the molecules highest occupied molecular orbital occurs after thermal treatment, indicating that the molecules are lying down.

  • 46.
    Palmgren, Pål
    et al.
    KTH, School of Information and Communication Technology (ICT), Microelectronics and Information Technology, IMIT.
    Szamota-Leandersson, Katolina
    KTH, School of Information and Communication Technology (ICT), Microelectronics and Information Technology, IMIT.
    Weissenrieder, Jonas
    KTH, School of Information and Communication Technology (ICT), Microelectronics and Information Technology, IMIT.
    Claesson, Thomas
    KTH, School of Information and Communication Technology (ICT), Microelectronics and Information Technology, IMIT.
    Tjernberg, Oscar
    KTH, School of Information and Communication Technology (ICT), Microelectronics and Information Technology, IMIT.
    Karlsson, Ulf O.
    KTH, School of Information and Communication Technology (ICT), Microelectronics and Information Technology, IMIT.
    Göthelid, Mats
    KTH, School of Information and Communication Technology (ICT), Microelectronics and Information Technology, IMIT.
    Chemical reaction and interface formation on InAs(111)-Co surfaces2005In: Surface Science, ISSN 0039-6028, E-ISSN 1879-2758, Vol. 574, no 2-3, p. 181-192Article in journal (Refereed)
    Abstract [en]

    We report a study of the initial interface formation of Co on InAs(1 1 1)A and B surfaces using high resolution photoelectron spectroscopy and scanning tunneling microscopy. We observe a strong chemical interaction between Co and, in particular, surface indium forming a metallic overlayer already below monolayer coverage. On annealed surfaces this overlayer agglomerates into islands, with a narrow size distribution. Furthermore, no two-dimensional electron gas is formed on InAs(1 1 1)A-Co in contrast to the clean surface.

  • 47. Panaccione, G.
    et al.
    Altarelli, M.
    Fondacaro, A.
    Georges, A.
    Huotari, S.
    Lacovig, P.
    Lichtenstein, A.
    Metcalf, P.
    Monaco, G.
    Offi, F.
    Paolasini, L.
    Poteryaev, A.
    Tjernberg, Oscar
    KTH, School of Information and Communication Technology (ICT), Material Physics, Material Physics, MF.
    Sacchi, M.
    Coherent peaks and minimal probing depth in photoemission spectroscopy of Mott-Hubbard systems2006In: Physical Review Letters, ISSN 0031-9007, E-ISSN 1079-7114, Vol. 97, no 11Article in journal (Refereed)
    Abstract [en]

    We have measured hard x-ray photoemission spectra of pure vanadium sesquioxide (V2O3) across its metal-insulator transition. We show that, in the metallic phase, a clear correlation exists between the shakedown satellites observed in the vanadium 2p and 3p core-level spectra and the coherent peak measured at the Fermi level. Comparing experimental results and dynamical mean-field theory calculations, we estimate the Hubbard energy U in V2O3 (4.20 +/- 0.05 eV). From our bulk-sensitive photoemission spectra we infer the existence of a critical probing depth for investigating electronic properties in strongly correlated solids.

  • 48. Panaccione, G.
    et al.
    Offi, F.
    Torelli, P.
    Vanko, G.
    Tjernberg, Oscar
    KTH, School of Information and Communication Technology (ICT), Microelectronics and Information Technology, IMIT.
    Lacovig, P.
    Guarino, A.
    Fondacaro, A.
    Nigro, A.
    Sacchi, M.
    Brookes, N. B.
    Monaco, G.
    Analysis of surface-bulk screening competition in the electron-doped Nd2-xCexCuO4 cuprate using x-ray photoemission spectroscopy2008In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 77, no 12Article in journal (Refereed)
    Abstract [en]

    We report core level and valence band photoemission results obtained for Nd2-xCexCuO4 (x = 0.15) single crystals and films by using both soft and hard x rays, hence, with tunable depth sensitivity. When using hard x rays only, we observe distinct and energy separated structures in the main 2p(5)3d(9)L peak of Cu 2p(3/2) and 2p(1/2) core levels, including the well screened features located at the high kinetic energy side, which were recently reported by Taguchi et al. [Phys. Rev. Lett. 95, 177002 (2005)]. By varying the photoelectron takeoff angle, we analyze the difference in the screening properties between surface and bulk, and we demonstrate the depth dependence of the electronic properties by following the evolution of the bulk-related peak. The possible influence of the surface conditions on the Cu 2p spectral features is also discussed.

  • 49. Papalazarou, E.
    et al.
    Gatti, Matteo
    Marsi, M.
    Brouet, V.
    Iori, F.
    Reining, Lucia
    Annese, E.
    Vobornik, I.
    Offi, F.
    Fondacaro, A.
    Huotari, S.
    Lacovig, P.
    Tjernberg, Oscar
    KTH, School of Information and Communication Technology (ICT), Material Physics.
    Brookes, N. B.
    Sacchi, M.
    Metcalf, P.
    Panaccione, G.
    Valence-band electronic structure of V2O3: Identification of V and O bands2009In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 80, no 15Article in journal (Refereed)
    Abstract [en]

    We present a comprehensive study of the photon energy dependence of the valence band photoemission yield in the prototype Mott-Hubbard oxide V2O3. The analysis of our experimental results, covering an extended photon energy range (20-6000 eV) and combined with GW calculations, allows us to identify the nature of the orbitals contributing to the total spectral weight at different binding energies, and in particular to locate the V 4s states at about 8 eV binding energy. From this comparative analysis, we conclude that the intensity of the quasiparticle photoemission peak, observed close to the Fermi level in the paramagnetic metallic phase upon increasing photon energy, does not have a significant correlation with the intensity variation in the O 2p and V 3d yield, thus, confirming that bulk sensitivity is an essential requirement for the detection of this coherent low-energy excitation.

  • 50. Polley, C. M.
    et al.
    Dziawa, P.
    Reszka, A.
    Szczerbakow, A.
    Minikayev, R.
    Domagala, J. Z.
    Safaei, S.
    Kacman, P.
    Buczko, R.
    Adell, J.
    Hårdensson Berntsen, Magnus
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Material Physics, MF.
    Wojek, Bastian M.
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Material Physics, MF.
    Tjernberg, Oscar
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Material Physics, MF.
    Kowalski, B. J.
    Story, T.
    Balasubramanian, T.
    Observation of topological crystalline insulator surface states on (111)-oriented Pb1-xSnxSe films2014In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 89, no 7, p. 075317-Article in journal (Refereed)
    Abstract [en]

    We present angle-resolved photoemission spectroscopy measurements of the surface states on in-situ grown (111) oriented films of Pb1-xSnxSe, a three-dimensional topological crystalline insulator. We observe surface states with Dirac-like dispersion at (Gamma) over bar and (M) over bar in the surface Brillouin zone, supporting recent theoretical predictions for this family of materials. We study the parallel dispersion isotropy and Dirac-point binding energy of the surface states, and perform tight-binding calculations to support our findings. The relative simplicity of the growth technique is encouraging, and suggests a clear path for future investigations into the role of strain, vicinality, and alternative surface orientations in (Pb,Sn)Se solid solutions.

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