Coexistence Of Rarita-Schwinger-Weyl Fermion And Spin-1 Excitation In Bi₄Ni₆S₄

In addition to Dirac and Weyl fermions,exotic massless fermions with nonzero Berry curvature fluxes may exist in condensed matter systems under the protection of crystal symme-try,for example,spin-1 excitations with threefold degeneracy and spin-3/2 Rarita-Schwinger-Weyl fermions.More recently,the theory of topological quantum chemistry has provided us with a convenient way to find the excitation 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 quasiparticles mentioned above coexist in Bi₄Ni₆S₄in space group I2₁3（No.199）,when spin-orbit coupling is considered.Their nontrivial topology results in a series of Fermi arcs connecting the projection of these excitations on（001）surface.