Six-fold degenerate fermions in PdSb₂

Pyrite-type cubic PdSb₂ possess six-fold degenerate fermions protected by the non-symmorphic symmetry. By measuring the magnetic field (H) dependence of the magnetic torque τ(H) in single crystalline PdSb₂, we observe the de Haas-van Alphen (dHvA) oscillations. In analyzing the the dHvA oscillations with H // [111] direction, five frequencies are identified: F_α = 100 T, F_β = 127 T, F_γ = 175 T, F_η = 338 T, and F_ξ = 436 T. By fitting the experimental data using the Lifshitz-Kosevich equation , the effective masses of these bands are obtained with m*_α = 0.062m₀, m*_β = 0.086m₀, m*_γ = 0.26m₀, m*_η = 0.34m₀, and m*_ξ = 0.42(m₀ is the free electron mass). Further analysis of the dHvA oscillations reveals that two of the lightest pockets (α and β) at the R point in the Brillouin zone exhibit non-trivial Berry phase (Φ^B_α = 0.91π and Φ^B_β = 0.83π). These are two of the six-fold degenerate bands at the Fermi level.