Effect of topology on quasiparticle interactions in the Weyl semimetal WP2

We compare two crystallographic phases of the low-dimensional ${\mathrm{WP}}₂$ to better understand features of electron-electron and electron-phonon interactions in topological systems. The topological $\ensuremath{\beta}$ phase, a Weyl semimetal with a giant magnetoresistance, shows a larger intensity of electronic Raman scattering compared to the topologically trivial $\ensuremath{\alpha}$ phase. This intensity collapses for $T<{T}^*=20\phantom{\rule{0.16em}{0ex}}\mathrm{K}$, which evidences a crossover in the topological phase from marginal quasiparticles to a coherent low-temperature regime. In contrast, the topologically trivial $\ensuremath{\alpha}$ phase shows more pronounced signatures of electron-phonon interaction, i.e., an enhanced phonon linewidth and deviations from conventional anharmonicity in an intermediate-temperature regime. These effects provide evidence for an interesting interplay of electronic correlations and electron-phonon coupling. Interband and intraband electronic fluctuations can be distinguish by the energy range of electronic Raman scattering and their temperature dependence. Furthermore, we demonstrate a decisive dependency on symmetry that is critical to understand their interplay.