  Topological semimetals have revealed a wide array of novel transport
phenomena, including electron hydrodynamics, quantum field theoretic anomalies,
and extreme magnetoresistances and mobilities. However, the scattering
mechanisms central to these behaviors remain largely unexplored. Here we reveal
signatures of significant phonon-electron scattering in the type-II Weyl
semimetal WP$_{2}$ via temperature-dependent Raman spectroscopy. Over a large
temperature range, we find that the decay rates of the lowest energy $A_{1}$
modes are dominated by phonon-electron rather than phonon-phonon scattering. In
conjunction with first-principles calculations, a combined analysis of the
momentum, energy, and symmetry-allowed decay paths indicates this results from
intraband scattering of the electrons. The excellent agreement with theory
further suggests that such results could be true for the acoustic modes. We
thus provide evidence for the importance of phonons in the transport properties
of topological semimetals and identify specific properties that may contribute
to such behavior in other materials.
