Ideal type-I Weyl phonons in BAsO4 with fewest Weyl points

Weyl materials exhibit topologically nontrivial electronic or phonon energy -band crossings, offering promising conditions for fabricating novel topological devices and investigating exotic electrical and thermal transport properties. Here, we employ first -principles calculations to analyze the phonon dispersion of the experimentally synthesized boron arsenate (BAsO4) material, revealing the presence of four ideal type -I Weyl points with topological charge C = +/- 1 within the first Brillouin zone. These Weyl points are precisely located in the kz = 0.0 plane and are constrained by the S4 symmetry. Notably, both the O -atom and As -atom terminated surfaces exhibit clean and distinct surface arcs, connecting a pair of Weyl points with opposite chirality. These surface arcs maintain considerable separation in momentum space and span a length of approximately 0.687 angstrom-1. Furthermore, we construct a three -band effective Hamiltonian to capture the Weyl-related phonon branches in BAsO4 and to discuss the conditions governing the generation of Weyl points. Our results present an operational material platform for exploring the intrinsic properties of phononic Weyl-related phenomena.