Exotic massless fermionic excitations with nonzero Berry flux, other than the Dirac and Weyl fermions, could exist in condensed matter systems under the protection of crystalline symmetries, such as spin-1 excitations with threefold degeneracy and spin-$3/2$ Rarita-Schwinger-Weyl fermions. Herein, by using the ab initio density functional theory, we show that these unconventional quasiparticles coexist with type-I and type-II Weyl fermions in a family of transition metal silicides, including CoSi, RhSi, RhGe, and CoGe, when spin-orbit coupling is considered. Their nontrivial topology results in a series of extensive Fermi arcs connecting projections of these bulk excitations on the side surface, which is confirmed by (001) surface electronic spectra of CoSi. In addition, these stable arc states exist within a wide energy window around the Fermi level, which makes them readily accessible in angle-resolved photoemission spectroscopy measurements.

中文翻译：

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过渡金属硅化物中的多种拓扑费米子

除Dirac和Weyl费米子外，具有非零Berry通量的外来无质量费米子铁电激发可能存在于凝聚态中，且受到晶体对称性的保护，例如具有三重简并和自旋三价的自旋1激发。$3/\mathrm{2个}$Rarita-Schwinger-Weyl费米子。在本文中，通过使用从头算密度函数理论，我们证明了这些非常规准粒子与I型和II型Weyl费米子共存于一系列自旋轨道的过渡金属硅化物中，包括CoSi，RhSi，RhGe和CoGe考虑耦合。它们的非平凡拓扑结构导致一系列宽泛的费米弧，这些费米弧将这些体激发的投影连接在侧面上，这由CoSi的（001）表面电子光谱证实。此外，这些稳定的电弧状态存在于费米能级附近的宽能量窗口内，这使得它们在角度分辨光发射光谱测量中易于访问。