高温超导体MgB $_2$中的声子Weyl节直线
Phononic Weyl Nodal Straight Lines in High-Temperature Superconductor MgB$_2$
摘要：
基于第一性原理计算，我们预言了具有AlB $_2$型中心对称晶格的超导MgB $_2$在其体声子谱上具有所谓的声子拓扑Weyl节线（PTWNL）.这些PTWNL可以被视为在三维布里渊区（BZ）内沿着$-$ H-K-H方向上的直线紧密对齐的无数外尔点（WP）。它们的拓扑非平凡的性质，证实了在垂直于这些线的平面上的Berry曲率分布的计算。这些线是非常独特的，因为它们正好位于镜像对称保护的BZ的高对称边界处，同时，直线横穿整个BZ，不同于已知的分类，包括节点环，节点链或网络，和节点环。在（10 $\bar{1}$ 0）晶体表面，PTWNL诱导的鼓面状非平凡表面态出现在由具有相反手性的PTWNL的投影线限定的矩形区域内。此外，当镜像对称性破缺时，双简并PTWNL进一步提升，形成一对手征相反的WP。我们的研究结果为今后MgB $_2$上拓扑声子的实验研究铺平了道路，并在一系列同构的AlB $_2$型金属二硼化物中得到了类似的结果。
英文摘要：
Based on first-principles calculations, we predict that the superconducting MgB$_2$ with a AlB$_2$-type centrosymmetric lattice host the so-called phononic topological Weyl nodal lines (PTWNLs) on its bulk phonon spectrum. These PTWNLs can be viewed as countless Weyl points (WPs) closely aligned along the straight lines in the $-$H-K-H direction within the three-dimensional Brillouin zone (BZ). Their topological non-trivial natures are confirmed by the calculated Berry curvature distributions on the planes perpendicular to these lines. These lines are highly unique, because they exactly locate at the high-symmetry boundary of the BZ protected by the mirror symmetry and, simultaneously, straightly transverse the whole BZ, in different from known classifications including nodal rings, nodal chains or nets, and nodal loops. On the (10$\bar{1}$0) crystal surface, the PTWNLs-induced drumhead-like non-trivial surface states appear within the rectangular area confined by the projected lines of the PTWNLs with opposite chirality. Moreover, when the mirror symmetry is broken, the double-degenerate PTWNLs are further lifted to form a pair WPs with opposite chirality. Our results pave the ways for future experimental study on topological phonons on MgB$_2$ and highlights similar results in a series of isostructural AlB$_2$-type metallic diborides.
机构、总结、中文摘要均由AI分析而来，可能存在错误，请以论文正文为准。
