ChemInform Abstract: Superconductivity and Crystal Structures of (Ba_1‐xK_x)Fe₂As₂ (x = 0—1).

Abstract

Superconductors D 8000Superconductivity and Crystal Structures of (Ba1-xKx)Fe2As2 (x = 0-1). -The title compounds are synthesized from stoichiometric mixtures of the elements (Al 2 O 3 crucibles, Ar, 823-1223 K) and characterized by powder XRD and electrical resistance measurements. The XRD patterns at room temperature are indexed with tetragonal body-centered unit cells according to the ThCr2Si2-type (space group I4/mmm) or with orthorhombic face-centered unit cells (space group Fmmm). Superconductivity occurs over the whole doping range with a maximum T C of 38 K at x ≅ 0.4. The superconducting transitions in the orthorhombic compounds (Ba0.9K0.1)Fe2As2 (TC ≅ 3 K) and (Ba0.8K0.2)Fe2As2 (TC ≅ 25 K) give strong evidence for a correlation of superconductivity with the distorted structure and thus, potentially with an antiferromagnetically ordered state. -(ROTTER, M.; PANGERL, M.; TEGEL, M.; JOHRENDT*, D.; Angew. Chem., Int. Ed. 47 (2008) 41, 7949-7952; Fachbereich Chem. Biochem.,

LiFeAs: An intrinsic FeAs-based superconductor withTc=18 K

“…6,7 The AeFe 2 As 2 phases become superconducting ͑maximum T c ϳ 37 K͒ with appropriate substitution of Ae atoms with alkali metals. 8,9 It was also found that isostructural compounds KFe 2 As 2 and CsFe 2 As 2 with formal ͑Fe 2 As 2 ͒ 1− layers were superconducting, having much lower T c 's of 3.8 and 2.6 K, respectively. 9 Moreover, the evolution from a superconducting state to a spin-density wave ͑SDW͒ state by chemical substitution was observed in K 1−x Sr x Fe 2 As 2 .…”

Experimental consequences of thes-wavecos(kx)cos(kyParish1, Hu2, Bernevig3 2008Phys. Rev. B11651062View full textAdd to dashboardCite

“…For the 1/T1 NMR spin relaxation rate, the inter-band contribution is consistent with the current experimental results, including a (nonuniversal) T 3 behavior and the absence of a coherence peak. However, the intra-band contribution is considerably larger than the inter-band contributions and still exhibits a small enhancement in the NMR spin relaxation rate right below Tc in the clean limit.Introduction -The recent discovery of iron-based superconductors with a transition temperature as high as 55K has stimulated a flurry of experimental and theoretical activity 2,3,4,5,6,7,8,9,10,11 . However, a conclusive observation of the pairing symmetry still remains elusive, with both nodal and nodeless order parameters reported in experimental observations.…”

“…Introduction -The recent discovery of iron-based superconductors with a transition temperature as high as 55K has stimulated a flurry of experimental and theoretical activity 2,3,4,5,6,7,8,9,10,11 . However, a conclusive observation of the pairing symmetry still remains elusive, with both nodal and nodeless order parameters reported in experimental observations.…”

Evidence for Two Energy Gaps in SuperconductingBa0.6K0.4Fe2As2Single Crystals and the Breakdown of the Uemura Plot

“…The emergence of (Ba,Sr) 1−x K x Fe 2 As 2 (FeAs-122) [17,18] hole-doped superconductors with transition temperature T c up to 38 K has enriched the research in this area. Although stoichiometric (undoped) BaFe 2 As 2 shares the same feature with undoped LnFeAsO of a spin density wave type magnetic order and a structural transition at similar temperatures [19,20], however, there are also some significant differences between the properties of FeAs-1111 and FeAs-122 superconductors.…”

“…[23], in superconductors with low superfluid density (ρ s ), T c scales linearly with ρ s ∝ λ −2 ab (0), this is actually not required by the BCS theory. However, it is found that the charge carrier density in FeAs-122 is an order of magnitude larger than those in FeAs-1111 systems [17,24]. Thus it is very interesting to know whether the Uemura plot is still satisfied in FeAs-122 superconductors.…”