Two-gap superconducting properties of alkaline-earth intercalated $A_{x}(NH_{3})Fe_{2}Se_{2}$ (A = Ba or Sr)

Yung-Yuan Hsu; Yu-Bo Li; Shou-Ting Jian; Gu-Kuei Li; Ming-Cheng Yang

doi:10.1088/0953-2048/29/3/035005

paper

Two-gap superconducting properties of alkaline-earth intercalated $A_{x} (N H_{3}) F e_{2} S e_{2}$ (A = Ba or Sr)

arXiv:1509.06455 · doi:10.1088/0953-2048/29/3/035005

Abstract

Superconducting properties were studied on high quality superconductors $B a_{x} (N H_{3}) F e_{2} S e_{2}$ ( $T_{c}$ = 39 K) and $S r_{x} (N H_{3}) F e_{2} S e_{2}$ ( $T_{c}$ = 44 K) prepared by intercalating Ba/Sr atoms into tetragonal $β$ -FeSe by liquid ammonia. The elongated c-axis and almost unchanged a-axis of $B a_{x} (N H_{3}) F e_{2} S e_{2}$ , comparing with $β$ -FeSe, suggested an unchanged intra- $F e_{2} S e_{2}$ -layer structure and the $T_{c}$ enhancement is due to a 3D to 2D-like Fermi surface transformation. The superconducting coherent lengths $ξ$ (0), Ginzburg-Landau parameters $κ$ and penetration depths $λ$ (0) obtained from the extrapolated lower and upper critical fields $B_{c 1}$ (0) and $B_{c 2}$ (0) indicates that both compounds are typical type-II superconductors. The temperature dependence of 1/ $λ^{2}$ (T) of $B a_{x} (N H_{3}) F e_{2} S e_{2}$ deduced from the low field magnetic susceptibility shows a two-gap s-wave behaviour with superconducting gaps of $Δ_{1}$ = 6.47 meV and $Δ_{2}$ = 1.06 meV.

Two-gap superconducting properties of alkaline-earth intercalated Ax​(NH3​)Fe2​Se2​ (A = Ba or Sr)

Abstract

Two-gap superconducting properties of alkaline-earth intercalated $A_{x} (N H_{3}) F e_{2} S e_{2}$ (A = Ba or Sr)