TY  - JOUR
A1  - Bisti, F.
A1  - Rogalev, V. A.
A1  - Karolak, M.
A1  - Paul, S.
A1  - Gupta, A.
A1  - Schmitt, T.
A1  - Güntherodt, G.
A1  - Eyert, V.
A1  - Sangiovanni, G.
A1  - Profeta, G.
A1  - Strocov, V. N.
T1  - Weakly-correlated nature of ferromagnetism in nonsymmorphic CrO\(_2\) revealed by bulk-sensitive soft-X-ray ARPES
JF  - Physical Review X
N2  - Chromium dioxide CrO\(_2\) belongs to a class of materials called ferromagnetic half-metals, whose peculiar aspect is that they act as a metal in one spin orientation and as a semiconductor or insulator in the opposite one. Despite numerous experimental and theoretical studies motivated by technologically important applications of this material in spintronics, its fundamental properties such as momentumresolved electron dispersions and the Fermi surface have so far remained experimentally inaccessible because of metastability of its surface, which instantly reduces to amorphous Cr\(_2\)O\(_3\). In this work, we demonstrate that direct access to the native electronic structure of CrO\(_2\) can be achieved with soft-x-ray angle-resolved photoemission spectroscopy whose large probing depth penetrates through the Cr\(_2\)O\(_3\) layer. For the first time, the electronic dispersions and Fermi surface of CrO\(_2\) are measured, which are fundamental prerequisites to solve the long debate on the nature of electronic correlations in this material. Since density functional theory augmented by a relatively weak local Coulomb repulsion gives an exhaustive description of our spectroscopic data, we rule out strong-coupling theories of CrO\(_2\). Crucial for the correct interpretation of our experimental data in terms of the valence-band dispersions is the understanding of a nontrivial spectral response of CrO\(_2\) caused by interference effects in the photoemission process originating from the nonsymmorphic space group of the rutile crystal structure of CrO\(_2\).
KW  - physics
KW  - electronic structure
KW  - half-metals
KW  - angle-resolved photoemission spectroscopy
KW  - band structure methods
KW  - DFT+U
KW  - condensed matter physics
Y1  - 2017
U6  - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-172251
VL  - 7
IS  - 4
ER  - 
TY  - JOUR
A1  - Feng, Yi
A1  - Zhou, Jiadong
A1  - Qiu, Honglin
A1  - Schnitzlein, Matthias
A1  - Hu, Jingtao
A1  - Liu, Linlin
A1  - Würthner, Frank
A1  - Xie, Zengqi
T1  - Boron‐Locked Starazine – A Soluble and Fluorescent Analogue of Starphene
JF  - Chemistry – A European Journal
N2  - A starlike heterocyclic molecule containing an electron‐deficient nonaaza‐core structure and three peripheral isoquinolines locked by three tetracoordinate borons, namely isoquinoline‐nona‐starazine (QNSA), is synthesized by using readily available reactants through a rather straightforward approach. This new heteroatom‐rich QNSA possesses a quasi‐planar π‐backbone structure, and bears phenyl substituents on borons which protrude on both sides of the π‐backbones endowing it with good solubility in common organic solvents. Contrasting to its starphene analogue, QNSA shows intense fluorescence with a quantum yield (PLQY) of up to 62 % in dilute solution.
KW  - conjugated molecule
KW  - electronic structure
KW  - luminescence
KW  - starazine
KW  - starphene analogue
Y1  - 2022
U6  - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-276423
VL  - 28
IS  - 29
ER  - 
TY  - JOUR
A1  - Charnukha, A.
A1  - Thirupathaiah, S.
A1  - Zabolotnyy, V. B.
A1  - Büchner, B.
A1  - Zhigadlo, N. D.
A1  - Batlogg, B.
A1  - Yaresko, A. N.
A1  - Borisenko, S. V.
T1  - Interaction-induced singular Fermi surface in a high-temperature oxypnictide superconductor
JF  - Scientific Reports
N2  - 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.
KW  - electronic structure
KW  - photoemission spectroscopy
KW  - iron pnictides
KW  - chalcogenides
KW  - ARPES
Y1  - 2015
U6  - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-151987
VL  - 5
IS  - 10392
ER  - 
TY  - JOUR
A1  - Fiedler, Sebastian
A1  - El-Kareh, Lydia
A1  - Eremeev, Sergey V.
A1  - Tereshchenko, Oleg E.
A1  - Seibel, Christoph
A1  - Lutz, Peter
A1  - Kokh, Konstantin A.
A1  - Chulkov, Evgueni V.
A1  - Kuznetsova, Tatyana V.
A1  - Grebennikov, Vladimir I.
A1  - Bentmann, Hendrik
A1  - Bode, Matthias
A1  - Reinert, Friedrich
T1  - Defect and structural imperfection effects on the electronic properties of BiTeI surfaces
JF  - New Journal of Physics
N2  - The surface electronic structure of the narrow-gap seminconductor BiTeI exhibits a large Rashba-splitting which strongly depends on the surface termination. Here we report on a detailed investigation of the surface morphology and electronic properties of cleaved BiTeI single crystals by scanning tunneling microscopy, photoelectron spectroscopy (ARPES, XPS), electron diffraction (SPA-LEED) and density functional theory calculations. Our measurements confirm a previously reported coexistence of Te- and I-terminated surface areas originating from bulk stacking faults and find a characteristic length scale of ~100 nm for these areas. We show that the two terminations exhibit distinct types of atomic defects in the surface and subsurface layers. For electronic states resided on the I terminations we observe an energy shift depending on the time after cleavage. This aging effect is successfully mimicked by depositon of Cs adatoms found to accumulate on top of the I terminations. As shown theoretically on a microscopic scale, this preferential adsorbing behaviour results from considerably different energetics and surface diffusion lengths at the two terminations. Our investigations provide insight into the importance of structural imperfections as well as intrinsic and extrinsic defects on the electronic properties of BiTeI surfaces and their temporal stability.
KW  - electronic structure
KW  - spin–orbit coupling
KW  - surface morphology
KW  - semiconductor surfaces
Y1  - 2014
U6  - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-119467
SN  - 1367-2630
VL  - 16
IS  - 075013
ER  - 
TY  - JOUR
A1  - Dauth, M.
A1  - Wiessner, M.
A1  - Feyer, V.
A1  - Schöll, A.
A1  - Puschnig, P.
A1  - Reinert, F.
A1  - Kuemmel, S.
T1  - Angle resolved photoemission from organic semiconductors: orbital imaging beyond the molecular orbital interpretation
JF  - New Journal of Physics
N2  - 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.
KW  - Dyson orbitals
KW  - electronic structure
KW  - PTCDA
KW  - AG(110)
KW  - density-functional theory
KW  - approximation
KW  - energies
KW  - monolayers
KW  - spectroscopy
KW  - NTCDA
KW  - ARPES
KW  - orbital imaging
KW  - photoemission spectroscopy
Y1  - 2014
U6  - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-115180
SN  - 1367-2630
VL  - 16
ER  -