新電子關聯122層狀過渡金屬(銥、鈀、鉑) 鍺鈣化合物系統的超導性質

Superconductivity in the new electron-correlated 122-layer system CaT2Ge2 (T = Ir, Pd, Pt)

黃俊豪(Chun-Hao Huang)

指導教授 ： 古煥球

國立清華大學/理學院/物理學系/碩士(2013年)

https://doi.org/10.6843/NTHU.2013.00560

摘要

在具有鋇鐵砷型四角體心立方結構(空間群I4/mmm)的新122層狀化合物銥鍺化鈣及鈀鍺化鈣，具有超導特性及超導相轉變溫度分別是5.4 K及2.5K。在準三元化合物系統銥鉑鍺化鈣(Ca(Ir1-xPtx)2Ge2)中，由於單斜(monoclinic)結構產生(空間群為P21),導致超導相轉變溫度隨著鉑的比例而遞減。從5.4K (x=0)，4 K (x=0.1)，3.2 K (x=0.2)到2.2 K (x=0.5)以及在鉑的比例大於0.6時,沒有發現超導特性。另外在具有單斜結構的鉑鍺化銥在2K以上沒有發現有超導特性。銥鍺化鈣會在出現超導特性是因為沿著C軸的正四面體IrGe4所產生的晶格場和準二維的層狀Ir-Ge-Ir雜交以及Ir-5d7自旋軌道交互作用。在準正交11層狀系統銥鉑鍺((Ir1-xPtx)Ge) (空間群為Pnma)超導相轉變溫度隨著鉑增加而遞減從4.8 (x=0)，3.6(x=0.1)到2.3(x=0.2)以及比例大於0.3時沒有發現超導特性。另外Matthias發現鉑鍺化合物的超導溫度為0.4 K。

關鍵字

超導性 ； 122系統 ； 鍺

並列摘要

Superconductivity were observed in the new 122-layer compounds CaIr2Ge2 (Tc = 5.4 K) and CaPd2Ge2 (Tc = 2.5 K) with the BaFe2As2-type body-centered-tetragonal structure (bct, space group I4/mmm). For the pseudoternary Ca(Ir1-xPtx)2Ge2 system, superconducting transition Tc decreases from 5.4 K for CaIr2Ge2 (x = 0), to 3.8 K for x = 0.1, 3.0 K for x = 0.2, 2.2 K for x = 0.5, and below 2 K for x ﹥0.5. In addition to bct phase, x-ray powder differation pattern show the appearance of non-superconducting monoclinic 122-phase (space group P21, a < b, β > 90o). No Tc above 2 K was observed for the monoclinic compound CaPt2Ge2. Higher Tc in the bct CaIr2Ge2 is due to a strong quasi-2D Ir-Ge-Ir 5dxz,yz-4p-5dxz,yz hybridization in the Ir-Ge layer with the squeezed-along-c-axis IrGe4 tetragonal crystal field and the Ir-5d7 spin-orbital interaction. For the orthorhombic (11) layer system (Ir1-xPtx)Ge (space group Pnma), Tc decreases from 4.8 K for IrGe (x = 0), to 3.6 K for x = 0.1, 2.3 K for x = 0.2 and below 2 K for x ≧ 0.3, with low Tc of 0.4 K reported for PtGe.

並列關鍵字

superconductivity ； 122-system ； germanide

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