二维沙漏外尔环：单层GaTeI族的理论与材料实现
Hourglass Weyl loops in two dimensions: Theory and material realization in monolayer GaTeI family
摘要：
二维（2D）系统中的节点环通常易受自旋轨道耦合（SOC）的影响。在这里，我们探讨了2D系统的一种类型的双退化的节点回路，是强大的SOC下，并具有沙漏型分散。我们提出了实现这种沙漏外尔环，其中涉及非对称晶格对称性的对称性条件。根据对称性，环可以在布里渊区中呈现不同的图案。基于第一性原理计算，我们确定单层GaTeI族材料作为一个现实的材料平台，实现这样的循环。这些材料具有围绕高对称点的单个沙漏外尔环。有趣的是，还有一个额外的螺旋轴使自旋轨道狄拉克点。我们表明，沙漏外尔环和狄拉克点是强大的各种应用应变下。通过破坏螺旋轴，狄拉克点可以转化为第二个外尔环。此外，通过打破滑动镜，沙漏外尔环和自旋轨道狄拉克点都可以转化为一对自旋轨道外尔点。我们的工作提供了指导和现实的材料候选人探索迷人的物理几种新颖的二维涌现费米子。
英文摘要：
Nodal loops in two-dimensional (2D) systems are typically vulnerable against spin-orbit coupling (SOC). Here, we explore 2D systems with a type of doubly degenerate nodal loops that are robust under SOC and feature an hourglass type dispersion. We present symmetry conditions for realizing such hourglass Weyl loops, which involve nonsymmorphic lattice symmetries. Depending on the symmetry, the loops may exhibit different patterns in the Brillouin zone. Based on first-principles calculations, we identify the monolayer GaTeI-family materials as a realistic material platform to realize such loops. These materials host a single hourglass Weyl loop circling around a high-symmetry point. Interestingly, there is also a spin-orbit Dirac point enabled by an additional screw axis. We show that the hourglass Weyl loop and the Dirac point are robust under a variety of applied strains. By breaking the screw axis, the Dirac point can be transformed into a second Weyl loop. Furthermore, by breaking the glide mirror, the hourglass Weyl loop and the spin-orbit Dirac point can both be transformed into a pair of spin-orbit Weyl points. Our work offers guidance and realistic material candidates for exploring fascinating physics of several novel 2D emergent fermions.
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