Microscopic Origins of Hydrodynamic Transport in Type-II Weyl Semimetal WP$_2$

The origins of hydrodynamic transport in strongly interacting Dirac and Weyl semimetals have remained elusive in theoretical descriptions and experimental measurements. We investigate the structure and microscopic properties of transport in WP$_2$, a type-II Weyl semimetal, to probe the emergence of hydrodynamic phenomena. We characterize the quantum behavior underlying the hydrodynamic transport regime as a function of temperature through ab initio calculations of the relevant microscopic scattering processes, including electron-phonon, electron-electron, and phonon-mediated electron-electron lifetimes. We present a fundamentally new approach to calculate phonon-drag, a mechanism that is invoked in numerous recent experiments, and remains the subject of active debate in the field. Further, we show unique and unexpected features of the lifetime-resolved Fermi surfaces of WP$_2$ in the hydrodynamic regime and quantify the degree of anisotropy in electron and hole pockets. This description of the microscopic dynamics in hydrodynamic systems like WP$_2$ indicates the importance of electron-phonon interactions in understanding connections between transport in hydrodynamic materials and strongly correlated quantum systems including unconventional metals and high $T_c$ superconductors.