| Summary: | 碩士 === 國立臺灣大學 === 物理研究所 === 102 === In the condensed matter research, the materials with strong spin-orbit coupling show many interesting phenomena, such as Rashba splitting, and topological surface state. Therefore, Bi2TeI with bismuth, an element with a strong spin-orbit interaction, may have interesting physical characteristics. In this work, we use density functional theory (DFT) to investigate the possible structural phases of Bi 2 TeI and &;#64257;nd out that Bi2TeI with C3v symmetry and structural stacking sequences (along its rotational axis): ABCABCAB and ABCBACAB have lower total energies. Each stacking sequence has three di&;#64256;erent combinations of two BiTeI sequences and one Bi bilayer, or called phases, TeBiI-Bi2-IBiTe, TeBiI-Bi2-TeBiI and IBiTe-Bi2-TeBiI phases. Additional calculation of the surface energy shows that both stacking sequences with TeBiI-Bi2-TeBiI phase and IBiTe-Bi2-TeBiI phase have one favor cleavage plane with lower surface formation energy but TeBiI-Bi 2 -IBiTe phase has two possible cleavage planes with lower surface energy. This result indicates there exist more than one likely cleavage plane to be found in the experiments for the latter phase. The electronic structures for bulk and/or surfaces of these Bi 2 TeI phases are calculated and as expected show the Rashba e&;#64256;ect. The maximum Rashba coupling strength among these electronic structures is 4.54 eV &;#730;A, from the surface with ABCBACAB stacking sequence and IBiTe-Bi 2 -TeBiI phase, which is larger than the reported Rashba e&;#64256;ect of BiTeI measured from the ARPES [1]. The surface projected density of state (PDOS) of theoretical relevant surfaces are also investigated which could be useful for a future comparison with the measured tunnelling spectra.
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