Contrasted Sn Substitution effects on Dirac line node semimetals SrIrO${}_3$ and CaIrO${}_3$

Perovskite-type iridates SrIrO${}_3$ and CaIrO${}_3$ are a Dirac line node semimetal protected by crystalline symmetry, providing an interesting playground to investigate electron correlation effects on topological semimetals. The effect of Sn doping was examined by growing SrIr${}_{1-x}$Sn${}_x$O${}_3$ and CaIr${}_{1-x}$Sn${}_x$O${}_3$ thin films epitaxially on SrTiO${}_3$(001) substrate using pulsed laser deposition. Upon Sn doping, the semimetallic ground state switches into an insulator. As temperature is lowered, the resistivity, $\rho (T)$, of SrIr${}_{1-x}$Sn${}_x$O${}_3$ above a critical doping level ($x_{$\text{c}$} \sim 0.1$) shows a well-defined transition from the semimetal to a weakly ferromagnetic insulator at $T=T_{\text{c}}$. In contrast, the $\rho (T)$ of CaIr${}_{1-x}$Sn${}_x$O${}_3$ with increasing $x$ shows a rapid increase of magnitude but does not show clear signature of metal-insulator transition in the temperature dependence. We argue that the contrasted behavior of the two closely related iridates reflects the interplay between the effects of electron correlation and disorder enhanced by Sn doping.