The microscopic origin of high carrier mobility in transition-metal diphosphides remains under debate, with proposed mechanisms including hydrodynamic electron flow and suppressed momentum relaxation associated with spin-momentum locking. $\mathrm{W}{\mathrm{P}}_2$ provides a useful platform for addressing this issue because it crystallizes in two polymorphs: monoclinic $\alpha \text{−}\mathrm{W}{\mathrm{P}}_2$, a topologically trivial semimetal, and orthorhombic $\beta \text{−}\mathrm{W}{\mathrm{P}}_2$, a type-II Weyl semimetal. Here, we grew high-quality α- and $\beta \text{−}\mathrm{W}{\mathrm{P}}_2$ single crystals with residual-resistivity ratios of 3700 and 4200, respectively. Electrical transport measurements yield carrier mobilities of $1.90\times {10}^5$ and $1.88\times {10}^5\mathrm{c}{\mathrm{m}}^2{\mathrm{V}}^{-1}{\mathrm{s}}^{-1}$ at 5 K for α- and $\beta \text{−}\mathrm{W}{\mathrm{P}}_2$, corresponding to transport lifetimes ${\tau }_t$ of $6.93\times {10}^{-11}$ and $1.38\times {10}^{-10}$ s. Low-temperature resistivity analysis shows that the data are better described by residual impurity scattering together with a phonon-drag-related contribution than by simple $T^2$ electron-electron or $T^5$ electron-phonon forms. Raman spectra show linewidth broadening and weak Fano-type asymmetry in selected phonon modes, indicating mode-dependent electron-phonon coupling. Analysis of the electronic Raman response gives quantum quasiparticle lifetimes ${\tau }_q$ of $4.25\times {10}^{-14}$ and $3.74\times {10}^{-14}$ s at 5 K for α- and $\beta \text{−}\mathrm{W}{\mathrm{P}}_2$, yielding ${\tau }_t/{\tau }_q=1632$ and 3698, respectively. To account for this large ${\tau }_t/{\tau }_q$, we propose that two mechanisms may play crucial roles: spin-orbit coupling (SOC), which suppresses backscattering for $k$ points near band extrema, and orbital-momentum locking (OML), which restrains large-angle scattering for $k$ points away from band extrema. These results provide a comparative view of carrier scattering in the two phases of $\mathrm{W}{\mathrm{P}}_2$ and suggest that SOC and OML are relevant to the high mobility in transition-metal diphosphides.

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• Carrier dynamics
• Electrical properties
• Electron-phonon coupling
• Lattice dynamics
• Phonons
• Spin-orbit coupling
• Single crystal materials
• Weyl semimetal
• Crystal growth
• Electron-correlation calculations
• Energy-dispersive x-ray spectroscopy
• First-principles calculations
• Raman spectroscopy
• Transport techniques
• X-ray diffraction