利用第一原理計算研究碘碲化二鉍的電子結構

Abstract

在當今凝態物理的研究哩，具有強自旋軌道耦合的材料展現了許多新穎的物理特性，因此具有強自旋軌道耦合的碘碲化二鉍材料可能帶有其他新穎的物理特性。在此我們利用密度泛涵理論去研究碘碲化二鉍的結構，而且發現碘碲化二鉍具有C3v對稱性且主要有六種不同的同素異構體，其中兩種同素異構體具有兩種不同的表面。在電子結構方面，部分的塊材及表面接展現了Rashba effect，最大的Rashba 耦合常數是 4.54 eV A

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 find 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 different 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 effect. The maximum Rashba coupling strength among these electronic structures is 4.54 eV ˚A, from the surface with ABCBACAB stacking sequence and IBiTe-Bi 2 -TeBiI phase, which is larger than the reported Rashba effect 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.