Relativistic topological molecular crystals
Relativistic topological molecular crystals
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发表时间：
2022
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通讯作者：
T. Yu;R. Arita;M. Hirayama
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作者：
T. Yu;R. Arita;M. Hirayama
由于分子间相互作用通常太弱而无法介导能带反转，因此拓扑相通常难以在分子固体中实现。然而，在这项工作中，我们提出非平凡电子拓扑可能普遍出现在一类含有间隙电子轨道和重元素的分子晶体中，由此自旋轨道耦合驱动间隙和分子轨道之间的能带反转。我们提供了寻找这种相对论拓扑分子晶体的指导方针，并利用第一性原理计算来说明具有代表性的候选k4 Ba 2 [SnBi 4]的非凡特征：(1)它具有沿多个方向的可切割表面，具有明显的拓扑边界态，没有悬垂键。(2)对外部压力或应变有较强的响应，在较低的压力下可以发生拓扑相变。(3)热电效率高，Seebeck系数高达240µVK−1,300 K时晶格导热系数约为0.22 ~ 0.23 Wm−1 K−1。(4)活跃的间隙轨道导致的超低功函数（2.2 eV）。我们的工作提出了在分子材料中实现拓扑相的途径。通过与声模的非谐波耦合，晶体的特性仅在30 cm−1左右。f，晶格导热系数κ l随温度的变化，基于非谐波声子的计算。
Topological phases usually are difficult to realize in molecular solids because the intermolecular interactions are in general too weak to mediate band inversion. In this work, however, we propose that nontrivial electronic topology may ubiquitously emerge in a class of molecular crystals that contain interstitial electron orbitals and heavy elements, whereby spin-orbit coupling drives band inversion between the interstitial and the molecular orbitals. We provide guidelines to hunt for such relativistic topological molecular crystals, and utilize first-principles calculations to illustrate the extraordinary characteristics of the representative candidate K 4 Ba 2 [SnBi 4 ]: (1) It hosts cleavable surfaces along multiple orientations, with pronounced topological boundary states free from dangling bonds. (2) Strong response to external pressure or strain, whereby topological phase transition may occur under relatively low pressure. (3) High-efficiency thermoelectricity, with the Seebeck coefficient as high as 240 µ VK − 1 , and the lattice thermal conductivity around 0.22 - 0.23 Wm − 1 K − 1 at 300 K. (4) Ultralow work function (2.2 eV) caused by the active interstitial orbitals. Our work suggests a pathway of realizing topological phases in molecular materials. The peculiarity of crystals via anharmonic coupling with acoustic modes, are merely around 30 cm − 1 . f , Lattice thermal conductivity κ l versus the temperature, based on the calculation of anharmonic phonons.