Lorentz-violating type-II Dirac fermion, as a new type of quasiparticles beyond the high-energy physics, has received intense attention recently. However, excellent candidate materials which contain sufficiently more type-II Dirac points near the Fermi level are still in scarcity. Here, we report a family of existing full-Heusler compounds, namely XMg 2 Ag (X = Pr, Nd, Sm), can serve as excellent Lorentz-violating type-II Dirac semimetals. We find they show several symmetry-protected nodal loops and triply degenerate nodal points (TDNPs) when spin–orbit coupling (SOC) is not considered. These fermions show clear nontrivial surface states. When SOC is included, the TDNPs transform into type-II Dirac points, characterized by Fermi arc surface states. The type-II DPs are protected by the C 4 v symmetry in the Γ– X path. Comparing with other type-II Dirac semimetals, XMg 2 Ag compounds have additional advantages including: (i) they co...

中文翻译：

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完全豪斯勒化合物XMg 2 Ag（X = Pr，Nd，Sm）中违反洛伦兹的II型狄拉克费米子

违反洛伦兹的II型狄拉克费米子是一种超越高能物理的新型准粒子，最近受到了广泛关注。但是，仍然缺乏稀有的，在费米能级附近包含足够多的II型狄拉克点的优良候选材料。在这里，我们报告了一系列现有的全Heusler化合物，即XMg 2 Ag（X = Pr，Nd，Sm），可以用作出色的违反Lorentz的II型Dirac半金属。我们发现，当不考虑自旋-轨道耦合（SOC）时，它们显示出几个受对称保护的节点环和三重简并节点（TDNP）。这些费米子显示出清晰的平凡表面状态。当包括SOC时，TDNP转换为II型Dirac点，其特征是费米弧表面状态。II型DP受Γ–X路径中C 4 v对称性的保护。