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A systematic investigation has been performed by synthesis and comprehensive characterization of a series of SmFe1-xCuxAsO0.8F0.2 bulks (x = 0 to 0.2). These samples are well characterized by structural, Raman spectroscopy, microstructural, transport, magnetic measurements, and supplementary calculations within density functional theory (DFT). The parent compound, SmFeAsO0.8F0.2 (Sm1111), exhibits a superconducting transition temperature (Tc) of approximately 54 K. The lattice volume (V) is increased with Cu substitution (x) without observing any impurity phase related to copper, which confirms the successful incorporation of Cu at Fe sites in the superconducting FeAs layers. These analyses are also well in agreement with Raman spectroscopy measurements and relevant DFT results. The superconducting transition is decreased systematically with copper doping and completely suppressed for 7% Cu-doped Sm1111 (x = 0.07). A large amount of Cu substitution (x greater than 0.07) has demonstrated the metal to insulate transition in the low-temperature range, and no impurity phase was observed even at high Cu doping levels (x = 0.2). The calculated critical current density of the parent sample is suppressed with copper substitution, suggesting the reduced pinning centers, sample density, and grain connections, as confirmed by the microstructural analysis. Our studies suggest that the substitution of Cu in the superconducting FeAs layer, resulting the enlargement of the lattice volume, is a source of strong disorder scattering, leading to the suppression of Tc and the emergence of metal-to-insulator, unlike the more successful carrier doping by nickel (Ni) or cobalt (Co), as previously reported., Comment: 40 pages, 16 Figures

AeAFe4As4 (Ae = Ca, A = K; 1144) having a transition temperature of 35 K is a stoichiometric family of iron-based superconductors (FBS). Here, we present a detailed study of a high-pressure synthesis of CaKFe4As4 bulks to investigate the impact of these conditions on the superconducting properties of the 1144 family. Additionally, these samples are also prepared by conventional synthesis method at ambient pressure (CSP) and studied the influence of impurities on the superconducting properties of CaKFe4As4. Structural, microstructural, transport and magnetization measurements have been performed to reach the final conclusions. Interestingly, the high-pressure synthesis of the parent CaKFe4As4 compound enhances the transition temperature (Tc) by 2 K and the critical current density (Jc) by one order of magnitude in the whole magnetic field range of 9 T than that of the 1144 bulks prepared by CSP. It suggests the improvement of the pinning centers and grain connections by the high-pressure synthesis approach. Interestingly, our results depict the superconducting onset transition temperature (Tconset) of this stoichiometric 1144 family is robust with the presence of the common 122 (CaFe2As2 or KFe2As2) impurity phases, which is a different behavior compared to other FBS families. However, these impurity phases reduce the grain connections and lead to the phase separation during the formation of the superconducting (1144) phase., Comment: 39 Pages, 16 Figures

Iron-chalcogenide superconductors display rich phenomena caused by orbital-dependent band shifts and electronic correlations. Additionally, they are potential candidates for topological superconductivity due to the band inversion between the Fe $d$ bands and the chalcogen $p_z$ band. Here we present a detailed study of the electronic structure of the nematic superconductors FeSe$_{1-x}$Te$_x$ ($0

The high-pressure growth technique generally plays an important role in the improvement of the sample quality and the enhancement of various physical and magnetic properties of materials. The high gas pressure technique provides a large sample space (10-15 cm) to grow various kinds of materials. In this paper, we introduce the high gas pressure and high-temperature synthesis (HP-HTS) technique that is present at our institute and is applied to the growth process of different kinds of superconducting materials, particularly iron-based superconductors. More details and the working principle of this HP-HTS technique are discussed. We have also demonstrated the current results based on the iron-based superconductors by using this unique HP-HTS technique. These results demonstrate the enhancement of the superconducting properties with the improved sample quality compared to the conventional synthesis process at ambient pressure., Comment: 12 pages, 8 figures