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

• Main Authors: Tsai, Sun-Ting, 蔡松庭
• Other Authors: Tang, Shu-Jung
• Format: Others
• Language: zh-TW
• Published: 2013
• Online Access: http://ndltd.ncl.edu.tw/handle/43107988512336462913

碩士 === 國立清華大學 === 物理系 === 101 === 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.