In addition to Dirac and Weyl fermions, exotic massless fermions with non-zero Berry curvature fluxes may exist in condensed matter systems under the protection of crystal symmetry, for example, spin-1 excitations with threefold degeneracy and spin-3/2 Rarita–Schwinger–Weyl fermions with fourfold degeneracy. More recently, the theory of topological quantum chemistry has provided us with a convenient way to find the existence of these quasi-particles. Herein, we have found a space group (No. 199) that may have both spin-1 excitations and spin-3/2 Rarita–Schwinger–Weyl fermions near the Fermi level. By using the ab initio density functional theory, we show that these unconventional quasi-particles mentioned above coexist in Bi4Ni6S4 in space group [Formula: see text] (No. 199), when spin-orbit coupling is considered. Their non-trivial topology results in a series of Fermi arcs connecting the projection of these excitations on (001) surface.

中文翻译：

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Bi4Ni6S4 中 Rarita-Schwinger-Weyl 费米子和自旋 1 激发的共存

除了狄拉克和外尔费米子之外，在晶体对称性的保护下，凝聚态系统中可能存在具有非零贝里曲率通量的奇异无质量费米子，例如具有三重简并性的自旋1激发和自旋3/2 Rarita-Schwinger ——具有四倍简并性的外尔费米子。最近，拓扑量子化学理论为我们提供了一种方便的方法来发现这些准粒子的存在。在这里，我们发现了一个空间群（第 199 号），它可能在费米能级附近同时具有自旋 1 激发和自旋 3/2 Rarita-Schwinger-Weyl 费米子。通过使用从头算密度泛函理论，我们证明了上述这些非常规准粒子共存于 Bi4你6小号4在空间群[公式：见正文]（No. 199）中，当考虑自旋轨道耦合时。它们的非平凡拓扑导致一系列费米弧连接这些激发在（001）表面上的投影。