Maximally charged single-pair multi-Weyl point phonons in P23-type BeH2

The realization of multi-Weyl systems with the minimum nonzero number of Weyl points and the maximum charge number remains challenging in topology physics. In this work, based on first-principles calculations, we propose that BeH2 is thermodynamically, mechanically, and dynamically stable in a cubic crystal structure with the P23 space group. Importantly, this is the first work to report the appearance of single-pair multi-Weyl point phonons with the maximum charge number in P23-type BeH2. Furthermore, the number and charge of the Weyl points and the phononic surface modes can be tuned by applying 1% and 2% uniaxial strains along the [100] and [111] directions, respectively. Finally, we report that clean charge-two single-pair triple-point phonons appear in P23-type BeH2 and investigate the related chiral phonon transition under the uniaxial strains.