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 ${\rho }_{xx}$($T,H$), Hall resistivity ${\rho }_{xy}$($T,H$), and quantum oscillations of the magnetization as a function of temperature at various magnetic fields for $\mathrm{Mo}{\mathrm{O}}_2$ with a monoclinic crystal structure. The band structure calculations show that $\mathrm{Mo}{\mathrm{O}}_2$ is a nodal-line semimetal when spin-orbit coupling is ignored. It was found that a large magnetoresistance reaching $5.03\times {10}^4\%$ at 2 K and 9 T, its nearly quadratic field dependence, and a field-induced up-turn behavior of ${\rho }_{xx}$($T$), the characteristics common for many topologically nontrivial as well as trivial semimetals, emerge also in $\mathrm{Mo}{\mathrm{O}}_2$. 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 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 $\mathrm{Mo}{\mathrm{O}}_2$, which may be due to the crystal symmetry breaking. These results highlight $\mathrm{Mo}{\mathrm{O}}_2$ as a platform for studying the topological properties of oxides.