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探索低维材料的新奇物性是当前凝聚态物理和材料科学基础研究的一个重要前沿. 应变是调控低维材料物性的一个重要手段. 相比于块体材料, 低维材料通常具有良好的力学柔韧性, 并表现出敏锐的结构-电子响应关系, 因此可以通过结构变形对材料电子性质进行有效调控. 本文主要目的是介绍二维材料中通过非均匀应变获得新奇物性的研究进展. 主要讨论两个效应, 即赝磁场效应和挠曲电效应. 具体来说, 通过解析理论、实验进展、计算模拟以及围绕这些效应的应用等方面介绍相关研究进展. 从计算模拟的角度看, 由于非均匀应变破坏了晶体的平移对称性, 基于周期性边界条件的量子力学计算方法如第一性原理不再适用. 本文将介绍一个专门用来模拟非均匀应变的原子级计算方法, 即广义布洛赫方法, 并简要介绍该方法的一些具体应用.
Low-dimensional material represents a special structure of matter. The exploring of its novel properties is an important frontier subject in the fundamental research of condensed matter physics and material science. Owing to its small length scale in one or two dimensions, low-dimensional materials are usually flexible in structure. This feature together with the prompt electronic response to structural deformations enable us to modulate the material properties via a strain way. The main purpose of this paper is to introduce the recent research progress of obtaining novel physical properties by inhomogeneously straining two-dimensional materials, with focusing on two effects, i.e., pseudomagnetic field effect and the flexoelectric effect. Of course, the influence of inhomogeneous strains on electrons is not limited to these two effects. Fundamentally, an inhomogeneous deformation breaks the symmetry of crystalline structure. This may serve as a start point to delineate the structural-properties relation. First, the symmetry breaking can eliminate the degeneracy of energy levels. Second, the symmetry breaking will also cause the heterogeneity of electronic and phonon properties in different parts of the material. In the paper, we also introduce a special method named the generalized Bloch theorem that is suitable for dealing with the inhomogeneous strain patterns at an atomistic level. From the perspective of atomistic simulation, due to the breaking of translational symmetry, the standard quantum mechanical calculations encounter fundamental difficulties in dealing with an inhomogeneous strain, e.g., bending and torsion. The generalized Bloch method overcomes such an obstacle by considering rotational and/or screw symmetries given by bending and/or torsion in solving the eigenvalue problem. As such, quantum mechanical calculations can be still conducted with a relatively small number of atoms. -
Keywords:
- two-dimensional materials/
- strain engineering/
- pseudomagnetic field/
- flexoelectricity/
- generalized Bloch theorem
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Zigzag Armchair LDA PBE LDA PBE Graphene 0.22 0.22 0.22 0.22 Silicene 0.19 0.19 0.19 0.19 Germanene 0.28 0.28 0.28 0.27 Stanene 0.27 0.26 0.27 0.26 
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