Angle-dependent nontrivial phase in the Weyl semimetal NbAs with anisotropic Fermi surface

We investigated the Landau-level structure in Weyl semimetal NbAs, in which a pair of band degenerate points (Weyl points) exists inside an anisotropic crescent-shaped Fermi surface. Through phase analysis of quantum oscillations in various magnetic-field directions, we found that the phase took various values between zero and π, reflecting variations of the energy dispersion in the extremal area. The nontrivial phase value around π is seen when the extremal plane was relatively far from the Weyl pairs and the double-minimum energy dispersion caused by the band inversion disappears inside the plane.