Mobility-controlled extremely large magnetoresistance in perfect electron-hole compensated α−WP2 crystals

Recent studies discovered that the binary transition-metal compounds ${A}_{x}{B}_{y}$ demonstrate extremely large magnetoresistance (XMR) under magnetic field $B$, for example, ${10}^{6}%$ in $\mathrm{PtB}{\mathrm{i}}_{2}$ and ${10}^{5}%$ in $\mathrm{WT}{\mathrm{e}}_{2}$. The underlying physical origins, however, are quite diverse, such as electron-hole balance, backscattering forbidden of Dirac/Weyl fermions, and high mobility. Here we experimentally find an ideal compound ($\ensuremath{\alpha}\ensuremath{-}\mathrm{W}{\mathrm{P}}_{2}$) where the perfect electron-hole compensation can be sustained within a large temperature range (from 2 to 100 K). The XMR of $\ensuremath{\alpha}\ensuremath{-}\mathrm{W}{\mathrm{P}}_{2}$ is measured as high as $8.74\ifmmode\times\else\texttimes\fi{}{10}^{5}%$ under 9 T $B$ at 2 K, but it is remarkably decreased from $8.74\ifmmode\times\else\texttimes\fi{}{10}^{5}%$ to 18% when the temperature is raised from 2 to 100 K; simultaneously, the mobility is decreased by more than two orders of magnitude. Magnetotransport characterizations show that MR is proportional to ${B}^{2}$ and the pronounced dHvA quantum oscillations come from the conventional Schr\"odinger fermions in $\ensuremath{\alpha}\ensuremath{-}\mathrm{W}{\mathrm{P}}_{2}$, which rules out the possibility of Dirac fermions. These evidences strongly suggest that XMR observed in binary ${A}_{x}{B}_{y}$ semimetals is mainly attributed to high mobility, rather than Dirac/Weyl fermions, or resonant electron-hole compensation. This work elucidates the underlying physical origin of XMR in these compounds.