Fe-family of superconductors: Influence of Ni dopant on the superconductivity in BaFe 2 As 2 crystal and the relaxation
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MRS Advances © 2019 Materials Research Society DOI: 10.1557/adv.2019.412
Fe-family of superconductors: Influence of Ni dopant on the superconductivity in BaFe2As2 crystal and the relaxation volume 1
Jacques Soullard * and Ilya G. Kaplan2 1
Instituto de Física, Universidad Nacional Autónoma de México, CDMX, México
2
Instituto de Investigación en Materiales, Universidad Nacional Autónoma de México, CDMX, México
ABSTRACT
The doped iron arsenides present outstanding properties, one of them is an unconventional superconductivity, an unusual coexistence of superconductivity and magnetism. We calculated the electronic structure of the pure and Ni-doped BaF e2As2 by the embedded cluster method at the electron correlation level; the latter is calculated through the second- order Møller Plesset perturbation theory. For the doped clusters, we calculated the relaxation of the first and second neighbors of the impurity by optimizing their positions in the cluster. The total electronic density is analyzed through natural bond orbitals and the population of each atomic orbital (basis function) is determined; the robustness of this determination is tested comparing results obtained for the unrelaxed and relaxed cluster. The orbital population analysis uncovers some properties of magnetism and superconductivity in BaFe2As2. From our results, linear elasticity allows us to estimate the relaxation volume of Ni impurity.
INTRODUCTION The iron pnictides and iron chalcogenides are classified into six groups of compounds presenting superconductivity (SC) with high critical temperature upon doping [1]. The most studied of these groups is the 122 system such as AFe 2As2 (with A = Ca, Sr, Ba, or Eu). In this system, SC was first detected by Co substitution of Fe in SrFe2As2 [2] and BaFe2As2 [3]. Later, it was discovered in Ni-doped BaFe2As2 [4]. *
Corresponding author, [email protected]
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High critical temperature SC is also induced by other d-metal substitutions like any elements in the Fe, Co, and Ni columns in the Periodical Table (except, so far, Os) [5] and appears also under hole doping in the plane of A atoms (e.g., Ba substitution by K [6]). Just after the discovery of the Fe-based superconductors, the density functional theory (DFT) calculations revealed the main features of the electronic structure of doped and undoped BaFe2As2 compounds. It was shown that they have a quite complicated band structure as it presents several disconnected Fermi surfaces [7,8]. Its properties come mainly from the 3d-orbitals of Fe and the electron pairing mechanism is assumed to be based on antiferromagnetic spin fluctuations [7]. Other pairing mechanism have been proposed like orbital fluctuations [9]. Theories of SC starting from a doped Mott insulator are also proposed [10]. A complete knowledge of
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