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تسجيل مستخدم جديدStructure, antiferromagnetism and superconductivity of the layered iron arsenide NaFeAs
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A new layered iron arsenide NaFeAs isostructural with the superconducting lithium analogue, displays evidence for the coexistence of superconductivity and magnetic ordering.
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The layered iron superconductors are discussed using electronic structure calculations. The four families of compounds discovered so far, including Fe(Se,Te) have closely related electronic structures. The Fermi surface consists of disconnected hole
and electron cylinders and additional hole sections that depend on the specific material. This places the materials in proximity to itinerant magnetism, both due to the high density of states and due to nesting. Comparison of density functional results and experiment provides strong evidence for itinerant spin fluctuations, which are discussed in relation to superconductivity. It is proposed that the intermediate phase between the structural transition and the SDW transition in the oxy-pnictides is a nematic phase.
We investigate the chemical substitution of group 5 into BaFe2As2 (122) iron arsenide, in the effort to understand why Fe-site hole doping of this compound (e.g., using group 5 or 6) does not yield bulk superconductivity. We find an increase in c-lat
tice parameter of the BaFe2As2 with the substitution of V, Nb, or Ta; the reduction in c predicts the lack of bulk superconductivity [1] that is confirmed here through transport and magnetization results. However, our spectroscopy measurements find a coexistence of antiferromagnetic and local superconducting nanoscale regions in V-122, observed for the first time in a transition-metal hole-doped iron arsenide. In BaFe2As2, there is a complex connection between local parameters such as composition and lattice strain, average lattice details, and the emergence of bulk quantum states such as superconductivity and magnetism. [1] L. M. N. Konzen, and A. S. Sefat, J. Phys.: Condens. Matter 29 (2017), 083001.
A new iron-based superconductor (Ca,Pr)FeAs2 was discovered. Plate-like crystals of the new phase were obtained and crystal structure was investigated by single-crystal X-ray diffraction analysis. The structure was identified as the monoclinic system
with space group P21/m, and is composed of two Ca(Pr) planes, anti-fluorite Fe2As2 layers, and As2 zigzag chain layers. Plate-like crystals composed of the new phase showed superconductivity with Tc ~20 K in both magnetization and resistivity measurements.
EuFe2As2 is a member of the ternary iron arsenide family. Similar to BaFe2As2 and SrFe2As2, EuFe2As2 exhibits a clear anomaly in resistivity near 200 K. It suggests that EuFe2As2 is another promising parent compound in which superconductivity may be
realized by appropriate doping. Here we report the discovery of superconductivity in Eu0.7Na0.3Fe2As2 by partial substitution of the europium site with sodium. ThCr2Si2 tetragonal structure, as expected for EuFe2As2, is formed as the main phase for the composition Eu0.7Na0.3Fe2As2. Resistivity measurement reveals a transition temperature as high as 34.7 K in this compound, which is higher than the Tc of Eu0.5K0.5Fe2As2.
The $kappa$-(ET)$_2$X layered conductors (where ET stands for BEDT-TTF) are studied within the dimer model as a function of the diagonal hopping $t^prime$ and Hubbard repulsion $U$. Antiferromagnetism and d-wave superconductivity are investigated at
zero temperature using variational cluster perturbation theory (V-CPT). For large $U$, Neel antiferromagnetism exists for $t < t_{c2}$, with $t_{c2}sim 0.9$. For fixed $t$, as $U$ is decreased (or pressure increased), a $d_{x^2-y^2}$ superconducting phase appears. When $U$ is decreased further, the a $d_{xy}$ order takes over. There is a critical value of $t_{c1}sim 0.8$ of $t$ beyond which the AF and dSC phases are separated by Mott disordered phase.
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