高聚合密度Sn/In2O3奈米複合材料超導性與電子傳輸; Superconductivity and electron transport properties of high packing fraction Sn/In2O3 nanocomposites

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题名:	高聚合密度Sn/In2O3奈米複合材料超導性與電子傳輸;Superconductivity and electron transport properties of high packing fraction Sn/In2O3 nanocomposites
作者:	陳耀韋;Yao-wei Chen
贡献者:	物理研究所
关键词:	臨界溫度;跳躍傳輸;奈米顆粒;穿隧傳輸;超導性;氧化銦;臨界磁場;I-V特性;不可逆磁阻;irreversible MR;I-V curve;critical magnetic field;indium oxide;superconductivity;nanoparticles;tunneling;hopping;critical temperature
日期:	2010-07-16
上传时间:	2010-12-08 14:23:25 (UTC+8)
出版者:	國立中央大學
摘要:	本論文探討由錫奈米顆粒與氧化銦奈米顆粒形成的奈米複合材料之超導性與電子傳輸的機制，藉由電阻率，磁化率和磁化強度實驗進行量測，使用Sn_A與Sn_B混入氧化銦，聚合密度分別為62.5 %及75 %，f=62.5 %的樣品共有三個而f=75 %的樣品則有六個。錫顆粒之間夾雜氧化銦顆粒的數目會影響超導電子對的傳輸。f=62.5 %的樣品中只有Sn_A出現電阻驟降的現象。而f=75 %則是當氧化銦比例來到15 %及20 %時，一顆錫奈米顆粒旁邊已有超過一顆的氧化銦奈米顆粒，使超導電子對穿隧傳輸機率變小但依然有電阻驟降的現象。f=62.5 %的Sn80In2O320_A及f=75 %的Sn75In2O325_B在低溫時電阻率會快速上升而沒有驟降的現象，我們使用熱激發跳躍式的電子傳輸模型來解釋此現象。在f=62.5 %的Sn_A中，發現其I-V特性異於其他八個樣品，在超導溫度之上的所有溫度皆線性增加至某一電流後驟減形成一轉折點，顯示電子在樣品中運動不受任何阻擾，此轉折點隨著溫度升高往較高的驅動電流移動，在轉折點之前的曲線斜率也隨著溫度升高變小，推測溫度造成穿隧位壘變大以及熱激發下使在價帶的電子跨過能隙激發至傳導帶進行傳導。磁阻率方面在所有樣品的高溫區發現不可逆磁阻，此不可逆行為隨著溫度升高、氧化銦比例增加和驅動電流變大而變明顯。 The transport characteristics and superconductivity of Sn/In2O3 nanocomposites were studied. The measurement of magnetic susceptibility, magnetization, and electron transport measurement were performed using the Quantum Design PPMS. The two set of Sn/In2O3 nanocomposites studied were prepared by mixing the Sn and In2O3 nanopartilces with different mass ratio and being cold compressed into pellets. The obtained nanocomposites have packing fraction f=62.5 %(three samples) and f=75 %(six samples), respectively. The number of In2O3 nanoparticles between Sn nanoparticles will affect the transport of superconducting pairs. Only the pure tin sample shows the phenomenon that the resistivity decrease rapidly in f=62.5 % samples. On the other hand, in f=75 % samples that when the ratio of In2O3 comes to 15 % and 20 %, there is more than one In2O3 nanoparticles around Sn nanoparticles. This result causes the tunneling probability of superconducting electron pairs becomes smaller but the system still exist the phenomenon of rapidly decreasing resistivity.When the samples which have the most ratio of In2O3(20 % for f=62.5 % and 25% for f=75 %), the resistivity increases rapidly instead of superconducting transition. We use hopping model to describe the electron transport of these two samples. We found two special phenomena on I-V curve of the f=62.5 % sample is named Sn_A. Upon the superconducting temperature, the curve increases linearly to a threshold point and then decreases rapidly shows that electrons move without hindrance. This threshold point shifts to higher excitation current with increasing temperature. The other one is that slopes before the threshold point become smaller with increasing temperature. The reason is supposed that the temperature will make the tunneling barrier become higher and it will excite electrons from valance band through the energy gap to conduction band for conducting. Irreversible MR curves were observed in the high temperature regime, this behavior will become apparent with increasing temperature, increasing excitation current and in the In2O3 rich samples.
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