金鋁合金中之電子-聲子散射時間之研究

Abstract

摘要 電子的量子傳輸效應是凝態物理中一個很重要的問題。而電子-聲子及電子-電子的交互作用是影響量子傳輸的兩個主要作用。到目前為止，在「無序系統」中這兩個作用由理論或實驗都還未得到明確的結論。 電子-聲子交互作用在金屬及超導體中密切地影響其導電性質。而非彈性的電子-聲子散射時間 是描述此作用的重要物理量之一。其定量分析是我們實驗的關鍵部分。在實驗和理論上，純金屬中 和溫度的關係已經很清楚。但在無序金屬中， 和溫度以及無序度的關係目前還不清楚。對 主要的理論預測是 以及 ， 是電子的彈性平均自由徑，它可以代表系統的無序程度。然而，理論所預測的不能完全解釋實驗結果。 我們利用理論及實驗上都已成熟的弱局域效應來取出 和溫度以及無序度的關係。實驗所用的物理系統是三維的金鋁合金厚膜。金、鋁的莫耳比介於2.2：1與1.3：1；對應的 介於6.3 與18.8 （估計值)；10K電阻率介於103.6 與31.3 。此外，樣品有超導性，其超導臨界溫度介於0.4~0.82K。製作樣品首先是用電弧熔爐把所需比例之金、鋁均勻燒熔起來，再置入熱蒸鍍系統中，使之沈積於玻璃基板上，形成2300~4200 的膜。此厚度已經超過電子的相位同調長度，所以將樣品視為三維系統。 經由量測固定溫度下的磁電阻（0.5~15K），並將實驗資料對弱局域效應所預測的磁電阻公式做曲線擬合（Curve Fitting），可以取出 以及其他物理參數。由擬合分析中標準誤差較小的實驗結果來看， ，P介於2.15與3.75之間。用現有理論還無法明確地解釋這些結果。 此外，我們量測樣品電阻率隨溫度的變化 （T=0.5~300K）來探討因無序而增強的電子-電子交互作用。在低溫下（液氦溫度附近），可發現到電阻率有一最小值後，反而隨溫度下降而上升。理論預測在三維系統中，電阻率變化會和溫度的平方根成正比。由實驗結果發現，金鋁合金在1~3.5K之間 。而等效的庫倫交互作用參數 可以從 的實驗資料中擬合分析得出。我們分析Au2.2Al-2樣品得到 等於 -0.7145，不同於一般導體的 值是介於0到1之間。

Abstract The quantum transport of electrons is a significant problem in condensed matter physics. There are two major interactions in the quantum transport: one is the electron-phonon interaction, the other is the electron-electron interaction. Currently, in disordered systems, there are no exact conclusions for these two interactions both in theorys and in experiments. The electron-phonon interaction closely affacts the conducting property in metals and superconductors. The inelastic electron-phonon scattering time is one of the important physical quantities to describe this interaction. The quantitative analysis of is the key part of our experiments. The temperature dependence of in clean system is clear. But the temperature dependence and disorderness dependence of in disordered systems is still not clear now. The main predictions in theories are and , where is the elastic mean free path of electron which can indicate the degree of disorder of the systems. However, these predictions could not explain the experimental results completely. We use the well-established Weak-Localization effect to extract relations of vs. temperature T and vs. . The physical systems adopted in experiments are three-dimensional Au-Al thick films. The mole ratios of Au and Al are tuned from 2.2:1 to 1.3:1. Coreesponding 's vary from 6.3 to 18.8 (evaluated). And 10K-resistivities vary from 103.6 到31.3 . In addition, Au-Al samples have superconductivity and their superconducting transtion temperatures are between 0.4K and 0.82K. The first step of fabricating samples is to alloy Au and Al homogeneously in needed mole ratio by arc-melting. Then put them into thermal evaporating deposition system and deposite films of 2300~4200 thick. The thucknesses are longer than phase coherent lengths of the electron in these systems, so we recognize these samples the three-dimensional systems. We have measured magnetoresistance at fixed temperatures (0.5~15K), and done curve-fitting for the experimental data with the equation of magnetoresistivity predicted in Weak-Localization effect. Considering the results with smaller fitting error, we found , where P =2.15 ~ 3.75. This result could not be explained clearly by current theories. In addition, we measured , T=0.5~300K, to study the disordered-enhanced electron-electron interaction. At low temperatures (near liquid helium temperature), we found increase along with decreasing T after a minimum value of resistivity. Theory predicts that will be proportional to square root of T in three-dimensional systems. We found in the range of T=1~3.5K for Au-Al alloys. And the effective Coulomb interaction parameter could be obtained from curve-fitting of the data. We analysed the data of sample Au2.2Al-2 and obtained equal to -0.7145, unlike between 0 and 1 in normal metals.