Charge compensation in extremely large magnetoresistance materials LaSb and LaBi revealed by first-principles calculations

By the first-principles electronic structure calculations, we have systematically studied the electronic structures of recently discovered extremely large magnetoresistance (XMR) materials LaSb and LaBi. We find that both LaSb and LaBi are semimetals with the electron and hole carriers in balance. The calculated carrier densities on the order of ${10}^{20}\phantom{\rule{0.28em}{0ex}}{\mathrm{cm}}^{\ensuremath{-}3}$ are in good agreement with the experimental values, implying long mean-free time of carriers at low temperatures and thus high carrier mobilities. With a semiclassical two-band model, the charge compensation and high carrier mobilities naturally explain: (i) the XMR observed in LaSb and LaBi, (ii) the nonsaturating quadratic dependence of XMR on an external magnetic field, and (iii) the resistivity plateau in the turn-on temperature behavior at very low temperatures. The explanation of these features without resorting to the topological effect indicates that they should be the common characteristics of all electron-hole compensated semimetals.