Superconducting properties were studied on high quality superconductors Bax(NH3)Fe2Se2 (Tc= 39 K) and Srx(NH3)Fe2Se2 (Tc = 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 Bax(NH3)Fe2Se2, compared with β-FeSe, suggests an unchanged intra- Fe2Se2-layer structure and the Tc enhancement is due to a 3D to 2D-like Fermi surface transformation. The superconducting coherent lengths (0), the Ginzburg-Landau parameters κ and penetration depths (0) obtained from the extrapolated lower and upper critical fields Bc1 (0) and Bc2 (0) indicate that both compounds are typical type-II superconductors. The temperature dependence of 1/l2(T) of Bax(NH3)Fe2Se2 deduced from the low-field magnetic susceptibility shows a twogap s-wave behavior with superconducting gaps of δ1 = 6.47 meV and δ2= 1.06 meV.
|期刊||Superconductor Science and Technology|
|出版狀態||已發佈 - 2016 1月 22|
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