Magnetotransport properties of the single-crystalline nodal-line semimetal candidates CaT X (T=Ag, Cd; X=As, Ge)

Topological semimetals are characterized by protected crossings between conduction and valence bands. These materials have recently attracted significant interest because of the deep connections to high-energy physics, the novel topological surface states, and the unusual transport phenomena. While Dirac and Weyl semimetals have been extensively studied, the nodal-line semimetal remains largely unexplored due to the lack of an ideal material platform. In this paper, we report the magnetotransport properties of the two nodal-line semimetal candidates CaAgAs and CaCdGe. First, the transport properties of our single crystalline CaAgAs agree with those of CaAgAs polycrystals. They can be explained by the single-band model, consistent with the theoretical proposal that only nontrivial Fermi pockets linked by the topological nodal-line are present at the Fermi level. Second, our CaCdGe sample provides an ideal platform to perform comparative studies because the theoretical calculation shows that it features the same topological nodal line but has a more complicated Fermiology with irrelevant Fermi pockets. As a result, the magnetoresistance of our CaCdGe sample is more than 100 times larger than that of CaAgAs. Through our systematic magnetotransport and first-principles band structure calculations, we show that our CaTX compounds can be used to study, isolate, and control the novel topological nodal-line physics in real materials.