Magnetotransport properties of compensated semimetal HfB₂ with high-density light carriers

We present a detailed magnetotransport study on HfB₂, a possible topological nodal-line semimetal. HfB₂ exhibits field-induced resistivity upturn and plateau behaviors at low temperature and high field, accompanying rather large magnetoresistance. The analysis of the field dependence of Hall and longitudinal resistivity shows that there are two kinds of carriers (electrons and holes) with almost same carrier concentrations and rather high mobilities in HfB₂. Above field-induced phenomena can be well explained by using the two-band model with compensation condition. Even the carrier concentration is significantly high (∼1.8 [Formula: see text] 10²¹ cm^-3) in HfB₂, much larger than other known topological semimetals with discrete Dirac nodal points, the electron-type carriers still have relatively small effective masses. In contrast to ZrB₂, the slightly increased effective mass in HfB₂ manifests the effect of enhanced spin-orbit coupling due to the large atomic number of Hf.