Correlated-electron perovskite ${\mathrm{CaIrO}}_3$ shows the topologically protected line node near the Fermi level, wherein the high-mobility Dirac electrons reach the quantum limit (QL) with the one-dimensionally (1D) dispersive $n=0$ Landau level (LL) state at a moderate magnetic field. In the QL, the longitudinal magnetoresistance (MR) shows an extreme anisotropy against the field $\left(B\right)$ direction in spite of nearly isotropic Dirac band dispersions. The resistivity for $B\parallel a$ shows an insulating behavior with the MR ratio exceeding $2000\%$ around 18 T, whereas the $B\parallel c$ MR always remains metallic. This is accounted for in terms of the large difference of Fermi velocity of the $n=0$ LL between $B\parallel a$ and $B\parallel c$ due to the $B$ direction dependent $5d$ orbital electron hopping, which triggers the different instability toward the charge density wave formation for the 1D $(\parallel B)$ dispersive $n=0$ LL.

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• Electrical properties
• Semimetals
• Numerical techniques
• Resistivity measurements