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博碩士論文 etd-0705106-204644 詳細資訊
Title page for etd-0705106-204644
論文名稱 Title |
以低溫比熱研究NbSe2之超導配對對稱態 Superconducting Paring State in NbSe2: A Low Temperature Specific Heat Study |
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系所名稱 Department |
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畢業學年期 Year, semester |
語文別 Language |
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學位類別 Degree |
頁數 Number of pages |
107 |
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研究生 Author |
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指導教授 Advisor |
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召集委員 Convenor |
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口試委員 Advisory Committee |
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口試日期 Date of Exam |
2006-06-17 |
繳交日期 Date of Submission |
2006-07-05 |
關鍵字 Keywords |
超導配對對稱態、低溫比熱 paring state, Low temperature specific heat, NbSe2 |
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統計 Statistics |
本論文已被瀏覽 5718 次，被下載 2203 次 The thesis/dissertation has been browsed 5718 times, has been downloaded 2203 times. |
中文摘要 |
傳統超導體可以以BCS 理論解釋(Tc<35K)，但隨著陸續發現 超導體的Tc 溫度之增加，BCS 理論已無法解釋所有超導體之超導 特性，故有其他理論之提出，如 d-波（d-wave）、線結( line nodes)、點結(the point nodes)、s +g 波( s +g wave)，以及雙能隙模型(two-gap)等。繼以two-gap 模型成功解釋MgB2 後，我們亦試圖以低溫比熱的方法量測2H-NbSe2，由其比熱行為的分析探討是否雙能隙模型也可成功應用於NbSe2。並據此分別得出兩個大小能隙值；且觀察到其電子比熱項(γT)的係數γ 與磁場H 的非線性關係。再者，由超導臨界溫度與上臨界磁場的關係圖可看出在低磁場時有正曲率的特性，此與在雙能隙超導體MgB2 所觀察到的一致。因 此，用雙能隙模型來解釋NbSe2 超導配對對稱態是優於用傳統 s-wave(BCS)及用線結(line nodes) 模型解釋的。 |
Abstract |
Conventional superconductor could be explained by BCS theory (for Tc<35K), but the BCS theory is not valid for all superconductors with theincrease of critical temperature (Tc) in the continuous discovery of new superconductors. Later on, other theories, such as d-wave, line nodes, the point nodes, the s +g wave, the two gap model, have been proposed. After successfully applying the two-gap model on MgB2, we try to measure the magnetic field dependence of low-temperature specific heat on 2H-NbSe2. Subsequently, analysis is focused on checking whether the two-gap model could also be applied to NbSe2 . Based on this model, the corresponding two gap values are obtained. The nonlinear field dependence of electronic specific heat coefficient is also observed. Moreover, the positive curvature in Hc2(T) is similar to that in the other two-gap superconductor MgB2. Thus, the two-gap model appears to describe the superconducting gap function of 2H-NbSe2 better than s-wave and line nodes models. |
目次 Table of Contents |
圖目錄…………………………………………………………………...i 表目錄…………………………………………………………………..v 第一章 簡介………………………………………………………….1 1. NbSe2結構與特性…………………………………………….1 2. 研究動機……………………………………………………..4 第二章 基本比熱理論……………………………………………..9 1.晶格比熱……………………………………………………....9 2.電子比熱……………………………………………………..10 3. Schottky 比熱………………………………………………...11 4. d-wave 模型預測…………………………………………….11 5. BCS 模型理論……………………………………………….12 6. 線結(line-node)模型………………………………………...13 7. 雙能隙(two-gap)模型…..…………………………………...14 第三章 實驗方法…………………………………………………..16 1. 樣品製作…………………………………………………..16 2. 熱脈衝弛張法比熱儀……………………………………..18 (1) 比熱儀系統......................................................................18 (2) 操作方法………………………………………………..23 (3) 操作原理………………………………………………..36 3. 超導量子干涉磁量儀(SQUID Magnetometer).................41 (1) 元件基本原理…………………………………………..41 (2) SQUID 磁量儀之操作特性…………………………….43 (3) 測量結果範例…………………………………………..47 第四章 實驗結果與分析…………………………………………49 1. X-ray 繞射相圖的分析………………………………………49 2.低溫比熱的測量……………………………………………...51 (1) 比熱儀器系統的校正………………………………….51 (2) 樣品比熱的測量與分析……………………………….56 第五章 討論與結論……………………………………………….84 1.實驗結果之比較……………………………………………...84 2. SQUID 磁量儀之M-T 的測量………………………………90 參考資料………………………………………………………………93 |
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