Speakers: E. Z. Kurmaev (Institute of Metal Physics, Russian Academy of Sciences, Yekaterinburg, Russia)
Place: Knihovna FZÚ, Cukrovarnická 10, Praha 6
Presented in English
Organisers:
Department of Magnetics and Superconductors
The results of resonant inelastic X-ray scattering (RIXS) measurements and density functional theory (DFT) calculations of Fe and Cu superconducting pnictides: REO1-xFxFeAs (RE = La, Sm) [1], LiFeAs, NaFeAs [2], CaFe2As2 [3], FeSex [4] and ACu2B2 (A = Ca, Sr, Ba; B = Sb, As) [5] are presented. The experimental RIXS spectra are found to be consistent with DFT calculations. Both theory and experiment show that for Fe-pnictides the Fe 3d-states dominate on the Fermi level and the low Hubbard d-band typical for correlated systems is not found. RIXS measurements at Fe L2,3-edges show that I(L2)/I(L3) intensity ratio is small, close to that of Fe-metal and quite different with respect to correlated FeO which is indicative of itinerant character of Fe 3d-electrons. The comparison of experimental RIXS spectra with LDA+DMFT (Local Density Approximation combined with Dynamical Mean-Field Theory) calculations [6] shows a good agreement between theory and experiment (with the average Coulomb repulsion U = 3÷4 eV and Hund’s exchange J = 0.8 eV) only when Fe 3d-As 4p hybridization is taken into account. This Fe 3d-As 4p hybridization weakens electron correlations and therefore one can conclude that FeAs-based superconductors belong to weakly or moderately weakly correlated systems. It is found for Cu-pnictides that the copper 3d states are fully occupied and buried deep in the valence band. According to RIXS measurements at Cu L2,3-edges, the I(L2)/I(L3) intensity ratio in Cu-pnictides is small, comparable with that of Cu-metal and much less than in CuO and superconducting cuprates (YBa2Cu3Ox and YBa2Cu4O8) which indicates for weakly correlated Cu 3d-states.
This work is supported by the Russian Science Foundation (Project 14-22-00004).
[1] E. Z. Kurmaev, R.G. Wilks, A. Moewes, N. A. Skorikov, Yu. A. Izyumov, L. D. Finkelstein, R. H. Li, and X. H. Chen, X-ray spectra and electronic structure of iron arsenide superconductors (RFeAsO1-xFx, R = La, Sm), Phys. Rev. B 78, 220503(R) (2008).
[2] E. Z. Kurmaev, J. McLeod, N. A. Skorikov, L. D. Finkelstein, A. Moewes, M. A. Korotin, Yu. A. Izyumov and S. Clarke, The electronic structure of LiFeAs and NaFeAs probed by resonant inelastic X-ray scattering, J. Phys.: Condens. Matter 21, 345701 (2009).
[3] E. Z. Kurmaev, J. A. McLeod, A. Buling, N. A. Skorikov, A. Moewes, M. Neumann, M. A. Korotin, Yu. A. Izyumov, N. Ni and P. C. Canfield, Electronic structure of CaFe2As2: contribution of itinerant Fe 3d-states to the Fermi level, Phys. Rev. B 80, 054508 (2009).
[4] E. Z. Kurmaev et al., X-ray emission spectra, electronic structure and structural models of FeSex, J. Phys.: Condens. Matter 21, 435702 (2009).
[5] J. A. McLeod, E. Z. Kurmaev, I. Perez, V. K. Anand, P. Kanchana Perera, D. C. Johnston, A. Moewes, Electronic structure of copper pnictides: Influence of different cations and pnictogens, PRB 88, 014508 (2013).
[6] V. I. Anisimov, E. Z. Kurmaev, A. Moewes, Yu. A. Izyumov, Strength of correlations in pnictides and its assesment by theoretical calculations and spectroscopy experiments, Physica C 469, 442 (2008).
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