銅鍺合金厚膜中電子-電子交互作用導致之量子傳輸現象之研究

Abstract

依導電性質將材料做分類，最基本的就是分為金屬與絕緣體。近幾年來，無序系統中的金屬-絕緣體是如何相互轉變，且其內部的傳導機制為何成了重要的課題。故我們這次是以實驗的方法來研究金屬-絕緣體轉變中偏金屬態和偏絕緣態這兩方面的量子傳輸性質。 本實驗的樣品是先以arc-melting將高純度的原料熔成塊材，再以低於5x10-6 torr的真空下蒸鍍於玻璃上，而得到均勻、厚度約3000-6000 A的銅鍺合金厚膜。我們成功地做出有系統地串連弱局域與強局域區間的CuxGe100-x厚膜，其電阻率在給定的溫度(2-300 K)下，隨著銅對鍺的莫耳比例減少而增加，顯示出該系統在低溫下的電子傳輸機制與溫度變化密不可分。當x較大時，即54≦x≦46，電阻率是隨著溫度減少的1/2次方而增加，除了顯示其為弱無序系統外，這結果支持其為電子-電子交互作用的理論預測，即□；當x較小時，即18≦x≦25，電阻率的增加是溫度的指數函數，在100 K以下可表為□ 。這結果則支持由Efros-Shklovskii 所提出之可變距離的跳躍式傳輸。綜合上述的觀點可得到的結論為：在低溫下的無序系統其傳導機制，是由隨無序程度改變之電子-電子交互作用所導致的。

The most fundamental classification of the electronic properties of a material is the separation into metallic and insulating states. In recent years, the problem of the metal-insulator transition in disordered systems and the undestanding of the conduction process itself has become important. In this work, we have experimentally studied the quantum transport properties on both the metallic and insulating sides. The CuGe films were prepared by arc-melting and thermal evaporation method in a vacuum of about torr onto glass substrates to form a film about 3000-6000 A thick. We have successfully obtained a series of thick CuxGe100-x films spanning the weakly and strongly localized regimes. With decreasing the mole concentration of Cu with respective to Ge, the resistivity of film becomes bigger at a given temperature (from 2 to 300 K) and demonstrates a stronger temperature dependence at low temperatures. As x is big, 54≦x≦46, resistivity increase with the square root of the decreasing temperature, implying a weakly disorder behavior. This behavior is due to the electron-electron interaction effects in three-dimensional disordered system. Our experimental results completely support the prediction of the theory, i.e.□. As x is small, 18≦x≦25, resistivity increases exponentially with decreasing temperature, implying a strongly localized behavior. When below 100 K, the resistivity rises exponentially, i.e.□ . This result indicates that the conduction is governed by the Efros-Shklovskii variable-range-hopping. These results show that the disorder enhanced electron-electron interactions dominate the low temperature transport in our films.