鐵基超導 鐵-硒-碲 之縱向與橫向霍爾電阻率之研究：釘扎效應與異常電傳輸性質

Longitudinal and Transverse Hall Resistivities in FeSe0.5Te0.5 Single Crystals : Pinning Effect and Anomalous Electrical Transport Properties

張景淵(Jing-Yuan Zhang)

指導教授 ： 王立民

國立臺灣大學/理學院/物理研究所/碩士(2015年)

https://doi.org/10.6342/NTU.2015.10310

摘要

本研究利用FeSe0.5Te0.5單晶樣品，量測其混合態及正常態之縱向電阻率及橫向電阻率(霍爾電阻率)。依據Anderson和Kim之理論，計算FeSe0.5Te0.5之活化能約400-1500 K，相對於其他超導體而言是比較低的，表示其釘扎力也較低。並計算其活化能與磁場之冪次關係，符合塑性渦旋蠕動模型。其橫向及縱向電阻率冪次關係之beta值約為1，並不符合W-T理論。由磁場平行c軸及磁場垂直c軸之電阻率計算出上臨界場不同向性γ值約等於1.61。依據Kohler’s rule討論FeSe0.5Te0.5正常態磁阻特性，FeSe0.5Te0.5系統不屬於費米液體。
本論文也研究利用RF磁控濺鍍系統製作FeSe0.5Te0.5薄膜。實驗配製不同成分比例之靶材及主要使用MgO基板，搭配不同的鍍膜參數，雖未成功沉積出超導薄膜，但由EDS分析來看，得知薄膜Te含量易受靶材成分之元素比例影響。要有效地控制薄膜組成比例使之達到Fe : Se : Te = 1 : 0.5 : 0.5，還需更一步研究。

關鍵字

鐵基超導 ； 霍爾效應 ； 超導混合態 ； 釘扎效應 ； 鐵-硒-碲薄膜

並列摘要

In this thesis, the in-plane longitudinal and Hall resistivities of superconducting FeSe0.5Te0.5 (FST) single crystals in the mixed state and the normal state were measured. According to Anderson-Kim theory, we calculated activation energy to be in 102 K order. The values of activation energy of FeSe0.5Te0.5 are relatively small than other superconductors, indicating a relatively weak vortex pinning.We also obtained a power law magnetic field dependence of activation energy which are within the plastic vortex creep model.The scaling behavior obtained with beta=1 is not in agreement with W-T theory.Anisotropic upper critical fields and coherence lengths with an anisotropy ratio of 1.61 have been deduced. The normal-state magnetoresistance were scaled by the Kohler’s rule.
In addition, we deposited FeSexTey films mainly on MgO substrates by radio frequency sputtering. Using different target of stoichiometry and by adjusting parameters, none of films reached zero resistance. EDS analysis revealed that the ratio of Te in films are subject to the composition of the target. To deposit FeSexTey films with Fe : Se : Te = 1 : 0.5 : 0.5 requires further works.

並列關鍵字

iron-based superconductor ； hall effect ； mixed state of superconductor ； pinning effect ； Fe-Se-Te flims

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