鐵硒超導體，具有簡單的結構，由鐵硒層一層層堆疊而成，是用來研究鐵基超導的機制很好的材料。然而，鐵硒與鉀鐵硒的母體化合物(parent compound)仍然是非常有爭議性的議題。在此篇論文裡，主要是以傳輸性質研究來支持，鉀鐵硒的母體化合物為不超導的鉀鐵硒(K2Fe4Se5)，並由鐵空缺的有序到無序的轉變誘發超導現象。在鐵硒奈米線的電性量測，金屬行為與絕緣體行為歸因於其具有Fe24Se25與Fe4Se5的鐵空缺相。在鉀鐵硒的樣品中，由電阻曲線可以擬合出不超導的鉀鐵硒(K2Fe4Se5)呈現二維Mott variable-range-hopping行為。超導鉀鐵硒的臨界磁場為93 (Tesla)，相干長度為1.77 (nm)。另外，鉀鐵硒中的有序的鐵空缺，可以由XRD的超晶格、高溫電組曲線的異常行為、磁性量測120K的轉變和磁滯曲線迴圈的大小而觀察到其明顯的變化，這些都說明了有序的鐵空缺會造成在120K有電荷或磁的有序行為。超導鉀鐵硒在磁阻量測上，超導樣品在200-95K，呈現線性行為，這可歸因於二能帶模型(two band model)貢獻與不超導相的負磁阻貢獻所疊加而來，或是由Abrikosov模型中，在量子極限中狄拉克態所造成的貢獻。超導鉀鐵硒在渦旋態(vortex state)時，磁阻在小磁場作用時，由於晶界的超導性被破壞而貢獻磁阻上升，接著由磁通蠕動使上升趨勢變緩，最後在大磁場下，渦旋不再被釘札效應所侷限，而產生渦旋流動，貢獻快速上升的磁阻。

FeSe superconductor withonly FeSe4 tetrahedral layer by layerstructure is an ideal candidate to investigated the mechanism of superconductivity.However, whether there exist the parent compounds for FeSe and potassium-intercalated FeSe have been controversial. In thisthesis, we have demonstrated by transport measurements that non-superconducting K2Fe4Se5 with Fe-vacancy ordered isthe parent compound of the superconducting K1-xFe2-ySe2, in which the superconductivity emerges after the iron vacancy becoming disorder.We also observed in theFe0.8Se nanowires both metallic and insulating behaviors in temperature dependence of resistance. This difference can also be attributed to the state of iron vacancy in Fe4Se5 and Fe24Se25 phases, respectively. The resistance of the non-superconducting K2Fe4Se5can be fit by the two-dimensional Mott variable-range-hoppingA pronounce transition at 120 K with hysteretic behavior is observed in this vacancy-ordered sample by magnetic measurement. This transition is associated with the presence of charge/spin order due to the iron vacancy order.The upper critical field of superconducting K1.9Fe4.2Se5 is about 93 Tesla, which corresponds to acoherence length of about 1.77 nm. Magnetoresistance (MR) measurements on superconducting K1.9Fe4.2Se5show linear dependencein magnetic field at temperatures between 90K-200K. We propose that this linear relationship comes from the combination of two-band model term and the negativeMR signals form Mott variable-range-hopping term (or the quantum limit of Dirac states proposed by Abrikosov.Detailed vortex studies show thatthere are non-negligible contribution from grain boundary to MR at low field, following by slow increase from thermal activated flux flow, and finally flux flows at high field.

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