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研究生:黃柏倫
研究生(外文):Bor-Luen Huang
論文名稱:超導層狀晶體結構中準粒子之傳輸性質
論文名稱(外文):Quasi-particle transport in an interlayer system
指導教授:牟中瑜
指導教授(外文):Chung-Yu Mou
學位類別:碩士
校院名稱:國立清華大學
系所名稱:物理學系
學門:自然科學學門
學類:物理學類
論文種類:學術論文
論文出版年:2001
畢業學年度:90
語文別:中文
論文頁數:66
中文關鍵詞:準粒子超導體超晶格c軸傳輸Andreev反射質量各向異性BdG方程式
外文關鍵詞:quasi-particlesuperconductorsuperlatticec-axis transportAndreev reflectionmass anisotropyBdG equation
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我們研究超晶格結構對高溫超導中準粒子在c軸方向傳輸的影響,特別是考慮由金屬/d-wave超導和絕緣體/d-wave超導所組成的超晶格系統 (NS 和 IS超晶格) 。我們發現,NS超晶格在金屬強各向異性極限下,低能量的態密度像是整塊d-wave超導的結果,除了態密度的極大值是發生在比原本能隙小的能量上。對於IS超晶格而言,這個極大值依然處在原來的位置。在此,我們提出了一種可以分辨NS超晶格和IS超晶格的方法,這是藉由在提供一個微小電流下比熱的測量。我們也計算在平面接觸測量中的非線性微分電導,發現在零偏壓下,Andreev尖峰的寬度也許是強烈的受到超晶格結構的影響,特別是,寬度會減小很多,這個效應是來自所有超導體的Andreev反射之間的破壞性干涉。這樣的寬度減小使得Andreev尖峰像是共振效應,而且已經在最近的實驗中被觀察到了。

We investigate the effect of the superlattice structure on the single particle transport along the c-axis of high temperature superconductors. In particular, superlattice systems that consists of metals/d-wave superconductors and insulators/d-wave
superconductors (NS and IS superlattice) are considered. We find
that for the NS superlattice in the large mass anisotropy limit of the metal, the density of state in the low energy section is bulk d-wave like except that the position of the quasi-particle peak can be considerably smaller than the gap value, while for the IS superlattice, the quasi-particle peak remains at the gap value. We suggest a possible way to distinguish the NS superlattice form the IS superlattice in the specific heat measurements by applying a small current. We also calculate the nonlinear differential conductance in the planar junction measurement. It is found that the width of the Andreev peak at zero-bias may be affected strongly by the superlattice structure, specifically, it can be considerably reduced due to the destructive interference of the Andreev reflections from all the superconductors. Such a reduction in the width makes the Andreev peak resonant-like and has been observed in a recent experiment.

1.Introduction
2.Density of State for Superconducting Superlattice
2.1 Density of State
2.2 Quasi-particle Momentum Without Bias
2.3 Symmetry Properties Between Electron-like and Hole-like Particle
2.4 Method
2.5 Homogeneous Case
2.6 Large mass anisotropy limit
2.7 Real case: YBCO
2.8 IS superlattice
2.9 Phase Difference
3.Nonlinear Differential Conductance for Superconducting Nulti-layer
3.1 Schematic Setup
3.2 Quasi-particle Momentum With Bias
3.3 Formula
3.4 Discussion
4.Conclusion
A.The structure of YBCO
B.Some useful terms denoted by dimensionless notations
C.The second order approximation for $\gamma\rightarrow 1$ in large mass anisotropic case

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