Proximity effects in topological insulators

由于最近在自旋轨道诱导的自旋动量锁定的电输运探测方面的实验进展和兴趣激增，我们建议对三维拓扑绝缘体中的邻近效应进行系统和全面的第一性原理计算，重点是Bi2Se_3系列，也包括一些新的结构。特别是，我们计划对狄拉克能带结构进行修正，并提取在所研究材料的表面态中出现的相关的邻近交换和自旋-轨道耦合。我们将使用常见的铁磁体和隧道势垒来模拟具有拓扑绝缘体的结，并评估不同结材料组成和隧道势垒厚度对邻近效应的影响。我们还期待着邻近效应的强磁各向异性。为了补充第一性原理的计算，我们将基于对称性论点建立现实的最小唯象模型来拟合和描述邻近能带结构，使得能够对由于铁磁电极而具有邻近区域的拓扑绝缘体的磁输运电荷和自旋进行大规模的数值模型计算。第一性原理和模型模拟都将提供对表面态、自旋和电荷输运重要的定性见解和定量信息。我们还预计，我们的工作将澄清一些紧迫的悬而未决的问题，这些问题对于解释最近的实验以及通过预测用于自旋注入和检测的最佳材料和结构参数以及自旋转移扭矩现象，将激励和指导新的实验。

Motivated by the recent experimental progress and surge of interest in the electrical transport detection of the spin-orbit induced spin-momentum locking, we propose to perform systematic and comprehensive first-principles calculations of the proximity effects in 3d topological insulators, focusing on the Bi2Se3 family, but also on some novel structures. In particular, we plan to establish modifications to the Dirac band structures and extract relevant proximity exchange and spin-orbit couplings emergent in the surface states of the investigated materials. We will use common ferromagnets and tunnel barriers to model junctions with topological insulators, and evaluate the proximity effects caused by different junction materials compositions and tunnel barrier thicknesses. We also expect strong magnetoanisotropies of the proximity effects. To supplement the first-principles calculations, we will build realistic minimal phenomenological models, based on symmetry arguments, to fit and describe the proximity band structures, enabling large-scale numerical model magneto-transport charge and spin calculations for topological insulators with proximity regions due to ferromagnetic electrodes. Both the first-principles and model simulations will provide qualitative insights and quantitative information important for surface states spin and charge transport. We also expect that our work will clarify some pressing unresolved issues important for the interpretation of recent experiments as well as motivate and guide new experiments by predicting optimal materials and structural parameters for spin injection and detection, and spin-transfer torque phenomena.