稳态强磁场下STM/STS图像的数值计算模拟

目前稳态强磁场中心已经实现在27 T强场下的STM成像。这就对强磁场下材料STM/STS图像的计算和理论分析提出了要求。当前，第一性原理方法在强磁场下的应用还有很多方法上的问题没有解决。基于在密度泛函计算和最大局域化瓦尼尔函数应用方面的经验，本项目拟发展具有第一性原理精度的强磁场下STM/STS图像模拟的新框架。以拓扑绝缘体Bi2Se3为研究对象，拟展开以下研究：1)通过最大局域化瓦尼尔函数计算，得到基于第一性原理计算的无磁场下的有效哈密顿参数。2)采用微扰展开方法引入强磁场效应，把磁场中的哈密顿参数展开为无磁场时的哈密顿参数，以及磁场相关的相因子的组合。进一步在哈密顿中引入自旋-轨道耦合修正。3)基于获得的磁场下的三维体结构和二维表面的哈密顿参数，使用迭代方法计算出半无限表面格林函数和表面局域态密度，通过Tersoff-Hamann近似得到拓扑绝缘体Bi2Se3表面的STM/STS图像。

Currently, STM images have been realized technically under 27 tesla at uniform strong magnetic field scientific center in China. This brings forth the requirement for STM/STS image calculations and theoretical analysis of materials under uniform strong magnetic field. For a direct first-principles calculation for system under strong magnetic field, now there are still unsolved methodology problems. Basing on our abundant research experience in the first-principles calculations and maximum localized Wannier functions (MLWF) approach, we try to build up a new theoretical research framework for STM/STS image calculation under uniform strong magnetic field. Taking topological insulator Bi2Se3 as an example, research contents are included: 1) Obtaining the effective Hamiltonian parameters for system without magnetic field by using the MLWF approach in combination with the first-principles calculations; 2) The effect of external magnetic field is introduced by perturbation theory. Here, the on-site energies and hopping parameters of system under a uniform steady magnetic field are expressed as a combination of those in the absence of magnetic field and an additional phase factor induced by magnetic field. Further, the spin-orbital coupling correction needs to be introduced in Hamiltonian under magnetic field. Diagonalizing the final Hamiltonian, one can get electronic structure and surface local density of states; 3) Based on Hamiltonian parameters of bulk system and slab system under magnetic field, one can obtain semi-infinite surface Green functions and surface local density of states by using iteration method. Eventually, high-precision STM/STS image can be obtained by Tersoff-Hamann approach.