Superconducting Fe-Based Compounds(A1−xSrx)Fe2As2with

Kalyan Sasmal

¹

,

Bing Lv

²

,

B. Lorenz

³

et al.

Abstract

New high-Tc Fe-based superconducting compounds, AFe2As2 with A = K, Cs, K/Sr and Cs/Sr, were synthesized. The Tc of KFe2As2 and CsFe2As2 is 3.8 and 2.6 K, respectively, which rises with partial substitution of Sr for K and Cs and peaks at 37 K for 50-60% Sr substitution, and the compounds enter a spin-density-wave state (SDW) with increasing electron number (Sr-content). The compounds represent p-type analogs of the n-doped rare-earth oxypnictide superconductors. Their electronic and structural behavior demonstrate the crucial role of the (Fe2As2)-layers in the superconductivity of the Fe-based layered systems, and the special feature of having elemental Alayers provides new avenues to superconductivity at higher Tc.

Understanding Doping, Vacancy, Lattice Stability, and Superconductivity in KxFe2−ySe2

“…And the predicted lattice constants a and c for K 0.5 Fe 2 Se 2 , 3.69 Å and 13.92 Å are consistent with the periods observed using scanning tunneling microscope along [110] and [001], 5.5 Å (√2a) and 14.1 Å,26 respectively, considering the calculation accuracy. It is worth noting that a similar trend of the changes in lattice parameters was observed in other electron‐doped ThCr 2 Si 2 structures, such as KFe 2 As 2 9, 44 and CaFe 2 As 2. 45 …”

“…The discovery of superconductivity in A x Fe 2− y Se 2 (A = K, Cs, Rb, Tl/Rb, Tl/K)1, 2, 3, 4, 5, 6 triggered another surge of research on iron‐based superconductors, which were previously only featured by iron pnictides7, 8, 9, 10, 11, 12 and β‐FeSe 13. The new series of superconductors can be regarded as the formation from the intercalation of metals between the FeSe layers of β‐FeSe.…”

Structural chemistry of superconducting pnictides and pnictide oxides with layered structures

“…Examples of such "hole doping" are the replacement of La 3þ by Sr 2þ in (La 1Àx Sr x )OFeAs (T c up to 25 K) [99] and substituting Ba 2þ by K þ in Ba 1Àx K x Fe 2 As 2 (T c up to 38 K) [23] or by Na þ in Ba 1Àx Na x Fe 2 As 2 (T c up to 34 K) [103]. Analogous substitutions of the alkaline earth by alkali ions in SrFe 2 As 2 [101] and CaFe 2 As 2 [102] have also been reported. Finally, it was found that even substitutions without changing the total electron count can induce superconductivity.…”

Electronic structures of ternary iron arsenides AFe2As2 (A = Ba, Ca, or Sr)

“…More recently, it was reported that the ternary iron-based arsenides AFe 2 As 2 (A=Ba, Ca, or Sr) become superconducting upon hole or electron doping [3][4][5][6]. Similar as in LaFeAsO [7,8], these ternary iron arsenides also exhibit a spin-density-wave-like anomaly and a structural transition from the tetragonal I4/mmm to the orthorhombic F mmm group at some temperature between 140 K and 200 K [9,10].…”