弱局域效應與交互作用對石墨烯載子傳輸特性的影響研究

Abstract

這個論文主要分成兩個部分：第一個部分是分析探討氫嵌入石墨烯在低溫下的磁阻性質;第二個部分是研究高溫超導與石墨烯所形成的約瑟芬接面。 石墨烯是當今熱門的二維材料，有著特別的電性傳輸。利用氫嵌入的方式，使得石墨烯與基板的鍵結減弱，來探討在低溫下，電子間交互作用與弱局域性效應在不同磁場範圍對導電性的修正。我們的分析顯示，磁場會改變電子間的交互作用的前因子，這個結果有待更多的研究來說明。 在臨界溫度以下，超導體的電阻會降至為零，這個奇特的性質吸引許多人投入研究。高溫超導不同於第一類型超導，有著更高的臨界溫度和對外加磁場有不同的反應。我們對於高溫超導/石墨烯/高溫超導的約瑟芬接面在臨界溫度下，是否能夠傳導超導電流感到興趣。我們成功地將化學氣相沉積法石墨烯貼在兩個臨近的超導上，然而並沒有看到超導電流。在低溫下，由於電極的非歐姆性質，電流與電壓曲線呈非線性。為了改善超導與石墨烯的接面與石墨烯本身的品質，我們使用電流來進行退火。除了第一次退火使得接面電阻下降之外，其他次的退火使得電阻越來越高，效果有限。

There are two subjects in this thesis. In the first part, I will report our study on the low temperature resistance properties of hydrogen-intercalated epitaxial graphene. Graphene is a fantastic material with lots of special properties. By means of hydrogen intercalation, the interaction between the substrate and graphene is reduced. At low temperatures, except the classic Drude conductivity, there are two quantum corrections: electron-electron interactions (EEI) and weak localization (WL). EEI and WL have different magnetic dependences. To study these two different properties ranges, we measured the sample in the low field and high field regime. The analysis shows that the prefactor of EEI is dependent of magnetic field, which need to be further studied. Second, we focused on the type-II superconductor. Superconductors can have no resistance below a critical temperature. This wonderful property has drawn many attentions. Type-II superconductor has higher critical temperature and has different magnetic properties compare to type-I superconductor. The proximity effect on YBCO-graphene-YBCO (SGS) junction was studied. We were interested in supercurrent in this SGS junction below the YBCO’s critical temperature. We successfully transferred a CVD graphene on the gap of the bridge. However, we did not observe the supercurrent in the junction. To improve the interface between superconductor and graphene and quality of the graphene, current anneal method was utilized, but had a limited effect.