Hidden type-II Weyl points in the Weyl semimetal NbP

A Weyl semimetal discovered recently, NbP, exhibits two groups of Weyl points with one group lying inside the k(z) = 0 plane and the other group staying away from this plane. All Weyl points have been assumed to be type I, in which the Fermi surface (Fs) shrinks into a point as the Fermi energy crosses the Weyl point. In this paper, we have revealed that the second group of Weyl points are actually type II, which are found to be touching points between the electron and hole pockets in the FS. Corresponding Weyl cones are strongly tilted along a line approximately 17 degrees off the k(z) axis in the k(x) - k(z) (or k(y) - k(z)) plane, violating the Lorentz symmetry but still giving rise to Fermi arcs on the surface. Therefore, NbP exhibits both type-I (k(z) = 0 plane) and type-II (k(z) not equal 0 plane) Weyl points.