Enhancement of the Magnetoresistance in the Mobility-Engineered Compensated Metal Pt₅P₂

The magnetoresistance (MR) in nonmagnetic materials continues to be a fertile research area in materials science. The search for giant, positive MR has been limited to a rather small window of materials such as high-mobility semimetals in single-crystalline form. Here, the observation of a very large positive MR in metallic Pt₅P₂ in polycrystalline form is reported. The observations reveal that improvement of the crystallinity results in a significant enhancement of the positive MR, exceeding 10 000% at 9 T, comparable to high-mobility semimetals. Based on first-principles calculations combined with magnetotransport and thermoelectric measurements, the Fermi surface of Pt₅P₂ is found to consist of a collection of multiple electron and hole pockets compensating one another, along with a characteristic pocket continuously connected to the adjacent Brillouin zone, together with possible topologically protected band crossings. This work extends the landscape of high MR candidate materials to polycrystalline metals, which demonstrates the importance of crystallinity and purity of the samples for the optimization of the MR.