類拓樸絕緣體之合金薄膜的自旋、電子與晶格結構研究

Study of spin, electronic, and lattice structures of a Quasi-Topological-Insulator allsy thin film

蔡松庭(Sun-Ting Tsai)

指導教授 ： 唐述中

國立清華大學/理學院/物理學系/碩士(2013年)

https://doi.org/10.6843/NTHU.2013.00565

摘要

過去的研究中發現鉛(1×1)薄膜在低溫時可以以單一晶域（Domain）平整成長在金/鍺（111）-(√3×√3)R30°的表面上，在這個研究中更進一步利用退火（Anneal）到室溫的方法，使潤濕層（Wetting Layer）中部分的金與鉛薄膜鍵結，在表面形成鉛金合金薄膜。
藉由改變光能量，我們區別了這個材料角解析光電子能譜（Angle-resolved Photoemission Spectrum, ARPES）中能帶的表面或塊材的特性。等能量面成像（Constant Energy Mapping）測量也使我們了解合金薄膜的表面態與基底、潤濕層、鉛薄膜、合金薄膜自身表面結構間的關係。
ARPES顯示合金薄膜的表面態表現出線性的色散關係，一般被稱為迪拉克錐（Dirac Cone）。材料能帶結構中的迪拉克錐在近年的許多研究中都顯示會有自旋結構，自旋解析光電子能譜（Spin-resolved Photoemission Spectrum, SRPES）也證實了這個薄膜的表面態在能帶結構表現出獨特的自旋與動量的相關性。
在這篇論文中我們也提出了室溫下摻雜金來更穩定有效率製備這個鉛金合金薄膜的方法。藉由一點一點摻雜少量的金，我們可以研究鉛金合金薄膜的成長過程。在成長過程中，ARPES的不同表面態消長以及低能量電子繞射（Low Energy Electron Diffraction, LEED）圖形的繞射亮點強度變化，提供了求解鉛金合金的結構中鉛、金比例的方法。

關鍵字

拓樸絕緣體 ； 合金 ； 薄膜 ； 迪拉克錐

並列摘要

The previous research shows that the thin film of Pb(1×1) structure could be stable in only single domain on the surface of the Au/Ge(111)- (√3×√3)R30° wetting layer at low temperature. In this research, we further make Pb atoms of the thin film bond with some of the Au atoms of the wetting layer, to form an alloy thin film on the surface of the Pb thin film by annealing it to room temperature.
With different photon energies, we distinguish the surface between bulk nature of the energy bands of this material by using angle-resolved photoemission spectroscopy (ARPES). Measuring constant energy contours, we can also realize the characters of the electronic states of the 2D alloy films.
Our measurement shows that the alloy thin film exhibits unique electronic structure of linear dispersion relation, which we usually call Dirac cone. The band structures of Dirac cones possess particular spin textures, which locks the spin polarization in the direction perpendicular to momentum. By using spin-resolved photoemission spectroscopy, we confirm that the electron states of Dirac cones of this alloy display particular chirality of their direction of spin and momentum.
In this thesis, we also propose an alternative method to prepare this alloy thin film by doping Au atoms to the Pb films annealed to room temperature. This method is not only more stable but also more effective. Doping of the Au atoms little by little, we can study the formation of the alloy thin film. In this process, the intensities of the surface states measured by ARPES as well as the diffraction spots measured by the low energy electron diffraction would correspondingly change, providing a way to know the ratio of Au to Pb atoms for this alloy film.

並列關鍵字

Topological Insulator ； Alloy ； Thin film ； Dirac cone

參考文獻

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