@article{DauthWiessnerFeyeretal.2014,
  author    = {Dauth, M. and Wiessner, M. and Feyer, V. and Sch{\"o}ll, A. and Puschnig, P. and Reinert, F. and Kuemmel, S.},
  title     = {Angle resolved photoemission from organic semiconductors: orbital imaging beyond the molecular orbital interpretation},
  series = {New Journal of Physics},
  volume    = {16},
  journal   = {New Journal of Physics},
  issn      = {1367-2630},
  doi       = {10.1088/1367-2630/16/10/103005},
  url       = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-115180},
  pages     = {103005},
  year      = {2014},
  abstract  = {Fascinating pictures that can be interpreted as showing molecular orbitals have been obtained with various imaging techniques. Among these, angle resolved photoemission spectroscopy (ARPES) has emerged as a particularly powerful method. Orbital images have been used to underline the physical credibility of the molecular orbital concept. However, from the theory of the photoemission process it is evident that imaging experiments do not show molecular orbitals, but Dyson orbitals. The latter are not eigenstates of a single-particle Hamiltonian and thus do not fit into the usual simple interpretation of electronic structure in terms of molecular orbitals. In a combined theoretical and experimental study we thus check whether a Dyson-orbital and a molecular-orbital based interpretation of ARPES lead to differences that are relevant on the experimentally observable scale. We discuss a scheme that allows for approximately calculating Dyson orbitals with moderate computational effort. Electronic relaxation is taken into account explicitly. The comparison reveals that while molecular orbitals are frequently good approximations to Dyson orbitals, a detailed understanding of photoemission intensities may require one to go beyond the molecular orbital picture. In particular we clearly observe signatures of the Dyson-orbital character for an adsorbed semiconductor molecule in ARPES spectra when these are recorded over a larger momentum range than in earlier experiments.},
  language  = {en}
}
@article{CharnukhaThirupathaiahZabolotnyyetal.2015,
  author    = {Charnukha, A. and Thirupathaiah, S. and Zabolotnyy, V. B. and B{\"u}chner, B. and Zhigadlo, N. D. and Batlogg, B. and Yaresko, A. N. and Borisenko, S. V.},
  title     = {Interaction-induced singular Fermi surface in a high-temperature oxypnictide superconductor},
  series = {Scientific Reports},
  volume    = {5},
  journal   = {Scientific Reports},
  number    = {10392},
  doi       = {10.1038/srep10392},
  url       = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-151987},
  year      = {2015},
  abstract  = {In the family of iron-based superconductors, LaFeAsO-type materials possess the simplest electronic structure due to their pronounced two-dimensionality. And yet they host superconductivity with the highest transition temperature T\(_{c}\)\(\approx\)55K. Early theoretical predictions of their electronic structure revealed multiple large circular portions of the Fermi surface with a very good geometrical overlap (nesting), believed to enhance the pairing interaction and thus superconductivity. The prevalence of such large circular features in the Fermi surface has since been associated with many other iron-based compounds and has grown to be generally accepted in the field. In this work we show that a prototypical compound of the 1111-type, SmFe\(_{0.92}\)Co\(_{0.08}\)AsO, is at odds with this description and possesses a distinctly different Fermi surface, which consists of two singular constructs formed by the edges of several bands, pulled to the Fermi level from the depths of the theoretically predicted band structure by strong electronic interactions. Such singularities dramatically affect the low-energy electronic properties of the material, including superconductivity. We further argue that occurrence of these singularities correlates with the maximum superconducting transition temperature attainable in each material class over the entire family of iron-based superconductors.},
  language  = {en}
}