鉍/鎳雙層薄膜和金/鉍/鎳三層薄膜之超導介面特性研究

Abstract

本研究首先利用磁控濺鍍製備出Bi/Ni雙層薄膜，並確定最佳條件為在基板溫度250˚C濺鍍Ni薄膜和在室溫下濺鍍Bi薄膜，並以80˚C退火。之後製備出Au/Bi/Ni多層薄膜以研究Au層和Bi/Ni雙層薄膜之間的介面。接著使用X光繞射儀(XRD)、穿透式電子顯微鏡(TEM)和能量色散X射線譜(EDS)對樣品進行分析，確認了Bi/Ni雙層薄膜中NiBi3的存在並觀察到Au/Bi/Ni多層薄膜中Au層部分擴散至Bi層中。 接下來取兩個Bi層厚度不同的Bi/Ni雙層薄膜和取兩個Au層厚度不同的Au/Bi/Ni多層薄膜樣品進行電性量測，透過R-T分析得到樣品的H_(c2,⊥) (0)、H_(c2,∥) (0)、ξ_⊥ (0)、ξ_∥ (0)和d_sc值，並且發現樣品Au20/Bi100中出現二次轉變，代表出現了NiBi3以外的未知超導來源；分析表面超導(Hc3)和H_(c2,∥) (0)的比值觀測不同厚度的Bi層和Au層對表面超導的影響；量測釘扎位能U/k_B 對外加磁場H之間的關係以及測量系統的Bereeinskii-Kosterlite-Thouless (BKT)相變來證明樣品(包含未知超導來源)的二維材料特性；量測磁阻發現所有樣品在低溫下具有弱反局域(Weak Anti-Localization，WAL)效應，所有Bi/Ni雙層薄膜在高溫下還同時具有一次方線性不飽和磁阻，證實NiBi3薄膜可能具有二維拓樸超導性質。

This study first prepared Bi/Ni bilayer films using magnetron sputtering, with optimal conditions determined as Ni film deposition at 250°C substrate temperature and Bi film deposition at room temperature, followed by 80°C annealing. Subsequently, Au/Bi/Ni multilayer films were fabricated to investigate the interface between Au layer and Bi/Ni bilayer. Through X-ray diffraction (XRD), transmission electron microscopy (TEM), and energy-dispersive X-ray spectroscopy (EDS) analyses, the presence of NiBi3 in Bi/Ni bilayer films was confirmed, and partial diffusion of Au layer into Bi layer was observed in Au/Bi/Ni multilayers. Electrical measurements were conducted on two Bi/Ni bilayer films with different Bi thicknesses and two Au/Bi/Ni multilayers with varying Au thicknesses. R-T analysis revealed parameters including H_(c2,⊥) (0), H_(c2,∥) (0), ξ_⊥ (0), ξ_∥ (0) and d_sc. A secondary transition was observed in the Au20/Bi100 sample, indicating an unknown superconducting source beyond NiBi3. The ratio of surface superconductivity (Hc3) to H_(c2,∥) (0) was analyzed to investigate the influence of Bi and Au layer thicknesses on surface superconductivity. Measurements of pinning potential U/k_B versus magnetic field H and Bereeinskii-Kosterlite-Thouless (BKT) transition characterization demonstrated two-dimensional material properties in all samples (including those with unknown superconducting sources). Magnetoresistance measurements revealed weak antilocalization (WAL) effects at low temperatures in all samples, while Bi/Ni bilayers additionally exhibited linear unsaturated magnetoresistance proportional to the first power at high temperatures, suggesting potential two-dimensional topological superconducting properties in NiBi3 films.