Quantum Transport Signatures of a Close Candidate for a Type II Nodal-Line Semimetal

The nodal-line semimetal is a new type of topological state of matter in which the crossing of two energy bands forms a nodal loop. In the absence of spin–orbit coupling, Mg₃Bi₂ is predicted as a type II nodal-line semimetal, which may evolve to a topological insulator with a small energy gap of ∼35 meV in the presence of spin–orbit coupling. However, the transport evidence is still lacking. Here, we measure the magneto-transport in Mg₃Bi₂. At low temperatures, the magnetoconductivity exhibits a weak antilocalization behavior. We fit the experimental data with a magnetoconductivity formula for the weak antilocalization effect of three-dimensional nodal-line semimetals as well as the well-known Hikami–Larkin–Nagaoka formula for two-dimensional weak (anti)­localization effects. By comparing the fitting results of these two theories, we demonstrate that the weak antilocalization in Mg₃Bi₂ is better described by the theory for nodal-line semimetals. Our work will inspire more explorations to use the new weak localization theory to identify a large spectrum of nodal-line semimetals.