鐵基超導體FeSe及Ba(Fe1-xCox)2As2的比熱研究

Abstract

我們對鐵基超導體11 系列-FeSe 單晶在磁場平行c 軸及平行ab 軸進行比熱量測。從比熱結果可以得知其超導溫度約為8 K，利用不 同的有序參數去擬合超導態電子比熱的結果，進一步獲悉了能隙上的 超導對對稱態。在費米面上同時存在了同向性(isotropic)s-wave 及異 向性(anisotropic)extended s-wave，而此結果與實驗數據γ(H)行為相 符。 除此之外，我們還對一系列的Ba(Fe1-xCox)2As2 單晶進行比熱量 測，成份為x=0, 0.08, 0.2。在成份為x=0.08 時，從電子比熱結果顯示 出超導溫度出現在Tc=21 K，而超導溫度隨著磁場的增加而降低。在 極低溫時，比熱明顯出現T2 項，提供了能隙上有節點的證據。因此， 我們可以知道Ba(Fe0.92Co0.08)2As2 為一能隙有節點之超導體。

We have measured the low-temperature specific heat of FeSe single crystals with in-plane and out-of-plane magnetic fields. The symmetry of the order parameter and the mixed state will be discussed for compounds. Coexistence of isotropic s-wave and anisotropic extended s-wave is found in FeSe. The mixed state γ(H) is also in accord with above findings. Also, we have measured the low-temperature specific heat of Ba(Fe1-xCox)2As2 (x=0,0.08,0.2) single crystals. The electronic specific heat of Ba(Fe0.92Co0.08)2As2 in the superconductiong state with Tc=21 K is revealed. A T2 term was observed at low temperatures, providing the evidence of nodes in the gap. Furthermore, the data suggest a nodal feature for Ba(Fe0.92Co0.08)2As2.