分子束磊晶成長鋁奈米薄膜中之拓撲相變與違反包立順磁極限之現象

Abstract

在這篇論文中，我將會報告利用分子束外延(molecular beam epitaxy)成長在砷化鎵(GaAs)上的鋁奈米薄膜(Al nanofilms)在低溫下表現的傳輸特性。利用此方法所成長的鋁奈米薄膜比傳統的鋁塊材擁有較高的臨界溫度與臨界磁場。特別的是，在這樣的鋁奈米薄膜中觀察到拓撲相變(topological transition)，這表示我們的鋁奈米薄膜可是被視為二維系統。另外也發現在最薄的樣品中(3-nm)平行的上臨界磁場(upper critical magnetic field)能夠超過包立順磁極限(Pauli paramagnetic limit)。

In this thesis, I shall report extensive transport measurements on aluminum (Al) nanofilms (as-grown thickness ranging from 3 nm to 4 nm) grown on GaAs by molecular beam epitaxy (MBE). Such MBE-grown Al nanofilms have a higher superconductor transition temperature (around 2.17 K, depending on the thickness) compared to that of bulk aluminum (1.2 K). In particular, I observed the topological transition of Berezinskii-Kosterlitz-Thouless (BKT) transition which implies two-dimensional superconductivity in our system. I also found that the upper critical field goes beyond the Pauli paramagnetic limit in the thinnest sample (3-nm thick).