Interstitial‐Electron‐Induced Topological Molecular Crystals
Interstitial‐Electron‐Induced Topological Molecular Crystals
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DOI：
10.1002/apxr.202200041
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发表时间：
2022-02
期刊：
影响因子：
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通讯作者：
Tonghua Yu;R. Arita;M. Hirayama
中科院分区：
文献类型：
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作者：
Tonghua Yu;R. Arita;M. Hirayama
与拓扑材料相比，分子固体的特征是具有大间隙的弱分散能带，通常无法到达拓扑相。然而，在这项工作中，提出了非平凡电子拓扑可能普遍出现在一类含有间隙电子态的分子晶体中，其能带容易与分子轨道的能带反转。提供了寻找这种间隙电子诱导的拓扑分子晶体的指南，特别是在拓扑绝缘状态下。由于分子晶体、间隙电子和拓扑性质的内在相互作用，它们表现出各种特殊的品质：1)它们可以沿多个方向承载可切割表面，具有明显的拓扑边界态，没有悬垂键。2)对中等机械扰动的强烈响应，在相对较低的压力下会发生拓扑相变。3)固有的高效率热电，由非抛物线带结构（因此具有高热功率），高移动的间隙电子（高导电性）和软声子（小晶格导热性）共同贡献。4)由于有活性的间隙电子，所以具有超低的功函数。利用第一性原理计算证明了具有代表性的候选材料K4Ba2[SnBi4]的这些特性。本研究提出了一种在体分子体系中实现拓扑相的途径，有望推动拓扑与分子材料的交叉研究。
Topological phases are usually unreachable in molecular solids, which are characterized by weakly dispersed energy bands with a large gap, in contrast to topological materials. In this work, however, it is proposed that nontrivial electronic topology may ubiquitously emerge in a class of molecular crystals that contain interstitial electronic states, the bands of which are prone to be inverted with those of molecular orbitals. Guidelines are provided to hunt for such interstitial‐electron‐induced topological molecular crystals, especially in the topological insulating state. They exhibit a variety of exceptional qualities, as brought about by the intrinsic interplay of molecular crystals, interstitial electrons, and topological nature: 1) They may host cleavable surfaces along multiple orientations, with pronounced topological boundary states free from dangling bonds. 2) Strong response to moderate mechanical perturbations, whereby topological phase transition would occur under relatively low pressure. 3) Inherent high‐efficiency thermoelectricity as jointly contributed by the non‐parabolic band structure (therewith high thermopower), highly mobile interstitial electrons (high electrical conductivity), and soft phonons (small lattice thermal conductivity). 4) Ultralow work function owing to the active interstitial electrons. First‐principles calculations are utilized to demonstrate these properties with the representative candidate K4Ba2[SnBi4]. This work suggests a pathway of realizing topological phases in bulk molecular systems, which may advance the interdisciplinary research between topological and molecular materials.