Extreme magnetoresistance in the topologically trivial lanthanum monopnictide LaAs

The family of binary lanthanum monopnictides, LaBi and LaSb, has attracted a great deal of attention as it displays an unusual extreme magnetoresistance (XMR) that is not well understood. Two classes of explanations have been offered for this: the presence of nontrivial topology and the compensation between electron and hole densities. Here, by synthesizing a new member of the family, LaAs, and performing transport measurements, angle-resolved photoemission spectroscopy, and density functional theory calculations, we show that (a) LaAs retains all qualitative features characteristic of the XMR effect but with a significant reduction in magnitude compared to LaSb and LaBi, (b) the absence of a band inversion or a Dirac cone in LaAs indicates that topology is insignificant to XMR, (c) the equal number of electron and hole carriers indicates that compensation is necessary for XMR but does not explain its magnitude, and (d) the ratio of electron and hole mobilities is much different in LaAs compared to LaSb and LaBi. We argue that the compensation is responsible for the XMR profile and the mobility mismatch constrains the magnitude of XMR.