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- W3118657232 abstract "In this thesis, we discuss the role of electronic Coulomb correlations in the spectral properties of iron and cobalt pnictides in the paramagnetic state. These materials belong to a new family of high-temperature superconductors discovered in 2008, with a maximum critical temperature of 56 K at present. The superconducting state emerges from the paramagnetic state, in which the electrons display many-body effects due to the importance of Hund’s coupling. This leads to middle-range renormalizations of the quasiparticle dispersion with an enhancement of the effective mass by a factor of 2 to 5, a finite quasiparticle lifetime, and a bad-metal behavior.Our work is based on the comparison between experimental data from angle-resolved photoemission spectroscopy (ARPES) and numerical calculations combining density functional theory (DFT) with dynamical mean-field theory (DMFT). Our theoretical technique is fully ab-initio, in the sense that all quantities are obtained from the experimental crystal structure of the material under consideration. In particular, we compute the value of the on-site Coulomb interaction by constrained-random phase approximation (cRPA) and take into account its frequency dependence. Furthermore, we go beyond the local density approximation (LDA) by including the effects of nonlocal screened exchange created by the Fock term of a Yukawa potential.We apply these techniques to the study of the electronic properties of transition-metal pnictides. We focus on three compounds: BaCo2As2 , CaFe2As2 and Ba2Ti2Fe2As4O. We calculate the spectral functions for all three materials and compare them directly to photoemission measurements, that we have taken in the case of CaFe2As2 . We demonstrate that the electron count in the metallic 3d correlated orbital is a key parameter for the strength of correlations and the coherence properties. In particular, we find a hole self-doping effect induced by the Ti2As2O layer that places the iron electrons of Ba2Ti2Fe2As4O in an incoherent state at 150 K, close to the physics of optimally-doped Ba0.6K0.4Fe2As2 . In contrast, we show that BaCo2As2 displays good Fermi-liquid behavior, which allows photoemission to capture a well-defined quasiparticle dispersion. We take advantage of this property to evaluate the antagonistic effects of the nonlocal screened exchange and of the frequency dependence of the dynamical Coulomb interaction. We find that neglecting both of them leads to an error cancellation which may produce a correct overall bandwidth. Conversely, one needs to take those effects into account for an accurate description of the Fermi surface and low-energy excitations, which are key to assessing the physics of BaCo2As2 and of pnictides in general." @default.
- W3118657232 created "2021-01-18" @default.
- W3118657232 creator A5027398903 @default.
- W3118657232 date "2014-10-23" @default.
- W3118657232 modified "2023-09-23" @default.
- W3118657232 title "Electronic Coulomb Correlations in Transition Metal Pnictides" @default.
- W3118657232 hasPublicationYear "2014" @default.
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