中文摘要
新122-層狀化合物SrIr2Ge2具有BaFe2As2之體心四方晶系結構(空間群I4/mmm)，其觀察到超導相轉變之最高溫度Tc為5.2 K，此溫度比同結構SrPd2Ge2的3.2 K高，卻比不穩定SrPt2Ge2的10.2 K低 [1]。由於在體心四方晶系結構中部分的Ir/Ge是無序的與非超導122-單斜相(空間群P21, a < b, β > 90o)的出現，使得準三元化合物Sr(Ir1-xPdx)2Ge2系統的Tc變化是複雜的。相轉變溫度從SrIr2Ge2的5.2 K平穩地降到2.8 K 於x = 0.6，並漸漸地增加到3.2 K於SrPd2Ge2。另外，11-正交晶系中層狀結構(Ir1-xPdx)Ge系統(空間群Pnma)，相轉變溫度從IrGe的4.8 K，降至4K與x = 0.1，最後低於2 K在x大於0.5時；而根據文獻，PdGe之超導相轉變溫度低於0.35 K [2]。在有序的層狀化合物SrIr2Ge2高Tc是來自於沿c軸的正四面體IrGe4產生的晶格場擠壓與122-體心四方晶系的準二維層狀Ir-Ge-Ir層5dxz,yz-4p-5dxz,yz耦合與自旋軌道交互作用。

Abstract
Superconductivity with a maximum Tc of 5.2 K was observed in the new 122-layer compound SrIr2Ge2 with the BaFe2As2-type body-centered-tetragonal (bct) structure (space group I4/mmm). Tc of 5.2 K is higher than the reported 3.2 K 122-bct SrPd2Ge2, but is lower than 10.2 K for the metastable bct SrPt2Ge2 [1]. For the pseudoternary Sr(Ir1-xPdx)2Ge2 system, variation of Tc is complicated by a partial Ir/Ge disorder in bct phase as well as the appearance of a non-superconducting 122-monoclinic phase (space group P21, a < b, β > 90o). Tc decrease steadily from 5.2 K in SrIr2Ge2, to a minimum of 2.8 K for x = 0.6, and then increases steadily to 3.2 K for SrPd2Ge2. For the 11-orthorhombic layer system (Ir1-xPdx)Ge (space group Pnma), Tc decreases from 4.8 K for IrGe to 4 K for x = 0.1 and below 2 K for x > 0.5, with no Tc reported down to 0.35 K for PdGe [2]. High Tc in the ordered SrIr2Ge2 layer compound is due to a strong quasi-2D 5dxz,yz-4p-5dxz,yz hybridization in the Ir-Ge-Ir layer with the squeezed-along-c-axis IrGe4 tetrahedral crystal field and Ir-5d spin-orbital interaction and is another example of multi-band (dxz/dyz/dxy) non-conventional s-wave superconductor.

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