銦/銀奈米顆粒複合系統之超導鄰近效應

Please use this identifier to cite or link to this item: http://ir.lib.ncu.edu.tw/handle/987654321/60724

Title:	銦/銀奈米顆粒複合系統之超導鄰近效應
Authors:	馬晨亮;Ma,Chen-liang
Contributors:	物理學系
Keywords:	超導;鄰近效應;Superconductor;proximity effect
Date:	2013-07-29
Issue Date:	2013-08-22 11:46:49 (UTC+8)
Publisher:	國立中央大學
Abstract:	本實驗以銦、銀奈米顆粒組成的複合系統作為零維超導鄰近效應實驗樣品。在實驗中我們藉由改變複合樣品的質量百分比並固定壓合密度以此觀測超導鄰近效應的強弱，共得到In100Ag0 ~ In16Ag84 十二種不同混合比例的樣品。由於鄰近效應發生的範圍需在超導相干長度之內，因此本次實驗採用奈米尺度的樣品來達到這項條件。奈米顆粒的製作備採用熱蒸鍍法，並以X光繞射實驗判定奈米顆粒的結構與粒徑。由共同體積函數擬合X光繞射譜圖後，可得知銦、銀奈米顆粒的平均粒徑分別為9 nm與9.6 nm。在超導性質的部分我們發現當樣品處於超導溫度以下時，抗磁強度將隨著複合樣品中銀比例的增加呈減弱的趨勢，這和典型鄰近效應中超導體會被正常導體的波方程干擾，進而導致超導性質變弱的情況相符。然而在樣品In80Ag00 ~ In40Ag60的區間中卻出現了逆鄰近效應的現象，抗磁強度不減反增，且在銀奈米顆粒的質量百分比為60％時達到極值。我們推測這是由於在正常導體內部的自由電子以安德烈夫反射的形式穿遂至超導體中，並形成古柏對使得超導體中的古柏對的總數增加所導致。在磁性的部份我們發現當銦與銀的質量比為4：6時，複合樣品的飽和磁化強度將會達到最大值。 In this thesis We study the superconducting proximity effect in the InxAg1-x nanocomposites. We obsver the superconducting proximity effect by measure the superconductivity and magnetic properties of In/Ag nanocomposites . When superconductor contact with normal metal, the proximity effect will change the density of state for both on boundary, but the superconducting proximity effect is only occurrence when sample size small than coherence length, hence we choose nanoparticles for sample. indium and silver nanoparticles were fabricated by thermal evaporation method. The mean diameters of indium and silver nanoparticles determined by XRD profile fittng to the size are 9 nm and 9.6 nm, respectively. The χ’(T) curves can fit to the Scalapino’s equation, giving the superconducting parameters such as Tc, χsc and λ0. The Tc doesn’t change significantly upon increasing the mass ration for Ag. Howerver, the superconductor diamagnetic screening signals show the inverse proximity effect occurred in In80Ag20 ～In40Ag60. We suggest this is due to free electronics tunneling from normal metal to superconductor, then causes the number of Cooper pairs is increasing.
Appears in Collections:	[Graduate Institute of Physics] Electronic Thesis & Dissertation

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