Fermi surface and de Haas-van Alphen oscillation in both the normal and superconducting mixed states of UPd₂Al₃

The dHvA oscillation was observed clearly in both the normal and superconducting mixed states for UPd₂Al₃ with the hexagonal structure. Eight kinds of dHvA branches were detected, which are well explained by the results of band calculations based on a fully-relativistic spin-polarized LAPW method. An inner orbit of a band 41-hole Fermi surface, named ζ, has the largest dHvA frequency of 9.45 × 10⁷ Oe and cyclotron mass of 65 m₀, reflecting a large electronic specific heat coefficient of 145 mJ/K²·mol. Branch α of a band 40-hole Fermi surface was observed in both the normal and superconducting mixed states, where the dHvA frequency does not change in magnitude between the normal and mixed states. The cyclotron effective mass of branch α is, however, found to be reduced and the corresponding Dingle temperature or scattering rate of the conduction electron increases with decreasing the field in the mixed state. An anisotropic energy gap with a line node for UPd₂Al₃ is discussed from the angular dependence of the dHvA amplitude in the mixed state.