金属铜的外尔半金属化
Turning Copper Metal into Weyl Semimetal
摘要：
由于需要非平凡的带连接性，导致电子的受保护的表面态，因此寻找新的拓扑量子系统是具有挑战性的。在这一领域的进展主要是由于实现了带反转机制之间的奇偶校验状态，这被证明是非常有用的，在预测许多这样的系统和我们了解他们的拓扑性质。尽管许多提出的材料假设s和p（或p/d，d/f）电子之间的带反转，在这里，我们探索了一种不同的机制，其中占据的d态受到四面体晶体场产生一个活跃的t2 g流形表现为一个有效轨道动量等于负1的状态，并在更高的能量推动jeff = 1=2的双重态。通过与可实现的最近邻轨道杂交，例如，在锌结构环境中，这允许奇宇称态的形成，其随后的带反转与未被占据的s带成为可能，促使我们寻找具有Cu+1离子态的化合物。利用化合价理论，结合材料数据库的检索，系统地研究了CuY（Y=F，Cl，Br，I）和CuXO（X=Li，Na，K，Rb）族化合物的电子结构和拓扑性质.我们的理论结果表明，CuF显示出一个理想的外尔半金属的行为特征与24外尔节点在体布里渊区。我们还发现另一种化合物CuNaO和CuLiO是s-d反转型拓扑绝缘体。它们的电子结构和相应的表面状态的结果，并在其拓扑性质的背景下进行了讨论。
英文摘要：
A search for new topological quantum systems is challenging due to the requirement of non{trivial band connectivity that leads to protected surface states of electrons. A progress in this field was primarily due to a realization of band inversion mechanism between even and odd parity states that was proven to be very useful in both predicting many of such systems and our understanding their topological properties. Despite many proposed materials assume the band inversion between s and p (or p/d, d/f) electrons, here, we explore a different mechanism where the occupied d states subjected to a tetrahedral crystal field produce an active t2g manifold behaving as a state with an effective orbital momentum equal to negative one, and pushing jeff = 1=2 doublet at a higher energy. Via hybridization with nearest neighbor orbitals realizable, e.g., in a zincblende structural environment, this allows a formation of odd parity state whose subsequent band inversion with an unoccupied s band becomes possible, prompting us to look for the compounds with Cu+1 ionic state. Chemical valence arguments coupled to a search in materials database lead us to systematically investigate electronic structures and topological properties of CuY (Y=F, Cl, Br, I) and CuXO (X=Li, Na, K, Rb) families of compounds. Our theoretical results show that CuF displays a behavior characteristic of an ideal Weyl semimetal with 24 Weyl nodes at the bulk Brillouin Zone. We also find that another compounds CuNaO and CuLiO are the s-d inversion type topological insulators. Results for their electronic structures and corresponding surfaces states are presented and discussed in the context of their topological properties.
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