Large magnetoresistance and nonzero Berry phase in the nodal-line semimetal MoO2

We performed calculations of the electronic band structure and the Fermi surface as well as measured the longitudinal resistivity ρxx(T,H), Hall resistivity ρxy(T,H), and quantum oscillations of the magnetization as a function of temperature at various magnetic fields for MoO2 with a monoclinic crystal structure. The band structure calculations show that MoO2 is a nodal-line semimetal when the spin-orbit coupling is ignored. It was found that a large magnetoresistance reaching 5.03 × 10^4% at 2 K and 9 T, its nearly quadratic field dependence, and a field-induced up-turn behavior of ρxx(T), the characteristics common for many topologically nontrivial as well as trivial semimetals, emerge also in MoO2. The observed properties are attributed to a perfect charge-carrier compensation, evidenced by both calculations relying on the Fermi surface topology and the Hall resistivity measurements. Both the observation of negative magnetoresistance for the magnetic field along the current direction and the nonzero Berry phase in de Haas–van Alphen measurements indicate that pairs of Weyl points appear in MoO2, which may be due to the crystal symmetry breaking. These results highlight MoO2 as a platform for studying the topological properties of oxides.