鈦鋁合金與鎳薄膜中低溫量子傳輸性質之研究

Abstract

摘要 電子在固體的傳導性質，一直是凝態物理中很重要的課題。在無序系統，電子-聲子的交互作用與電子-電子的交互作用，由於受到很強的雜質散射，在理論上，不是很好瞭解。所以我們透過實驗上的研究，探討電子-聲子的散射時間及電子-電子交互作用。 我們成功的製作一系列Ti73-xAl27Snx（x = 0-5）三維合金樣品，量測其低溫（2-22 K）磁電阻（磁場由0-1 T）。雜質Sn摻入Ti73Al27的多寡是我們的控制變因，並且此會提高自旋-軌道效應，但不會改變電阻率（r ~ 220 mohm cm），此外，樣品的高電阻率使得電子平均自由徑小至趨近於核的間距，結果ql ~ 0.0056 T（q是熱聲子波數，T是溫度，l 是電子彈性平均自由徑）。由八個合金樣品，我們量出61個磁電阻數據並將之比較於弱局域效應的磁電阻函數，引出相位破壞的散射時間。得到電子-聲子的散射率和溫度平方成正比。這個觀察還不能由目前無序系統中電子-聲子交互作用理論所瞭解。 除此之外，我們也製作一系列Ni（120 埃） 薄膜樣品，摻入Ag或Au （0-5 埃）。我們希望藉由低溫量測（0.35~25 K），探討自旋-軌道效應對電子-電子交互作用的影響。結果得到，電阻會隨溫度下降而增加，並成對數關係（dR ~ -ln T），符合電子-電子交互作用的修正。更進一步，我們還觀察到，在很低溫時（0.35-4 K），隨著雜質成分的增加，dR對 lnT的斜率也會輕微的增加。結論，自旋-軌道散射效應對於電子-電子交互作用有個很小但卻也不可忽略的影響。

Abstract Electrical conduction is a very important research topic in condensed matter physics. In disordered systems, the electron-phonon interaction and the electron-electron interaction in the presence of strong impurity scatting are not very well understood theoretically. In this work, we have experimentally studied the electron-phonon scatterng times and the electron-electron interaction effects. We have successfully measured the magnetoresistivities of crystalline disordered Ti73-x Al27Snx (x=0-5) alloys between 2-22 K and in magnetic fields up to 1 T. Impurity tin atoms are gradually introduced into the Ti73Al27 phase so that the spin-orbit scattering in the samples is adjusted in a controllable manner, while leaving the amounts of disorder ( i.e., resistivities r ~220 mohm cm ) of the sample barely changed. The resistivities of our samples are so high that the electron elastic mean free path approaches the interatomic spacing, resulting in a very small value of ql ~ 0.0056 T (q is the wavenumber of the thermal phonons, and T is the temperature). Based on as many as about 60 measurements on the various alloys, we have compared our results with weak-localization theory to extract dephasing times. We conclude that electron-phonon scattering rate varies with the square of temperature, in the dirty limit ( ql<<1 ). This observation cannot be understood in terms of the current theoretical concept for electron-phonon interaction in disordered metals. In addition, we have fabricated a series of thin Ni films (120 A) with minute amounts ( 0-5 A) of Ag or Au doping. By measuring R(T) at low temperatures（0.35 ~ 25 K）, we have studied the influence of spin-orbit scattering on the electron-electron interaction effects. Our results show that R increases logarithmically with decreasing temperature (dR(T) ~ -lnT), which is due to electron- electron interaction effects. Moreover, the rate of change in resistance dR with respective to lnT between 0.35 and 4 K increases slightly with increasing impurity concentration. We conclude that spin-orbit scattering effect has a small but not negligible influence on the e-e interaction in disordered systems.