Field direction dependent quantum-limit magnetoresistance of correlated Dirac electrons in perovskite CaIrO3

Correlated-electron perovskite CaIrO3 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 (B) direction in spite of nearly isotropic Dirac band dispersions. The resistivity for B∥a shows an insulating behavior with the MR ratio exceeding 2000% around 18 T, whereas the B∥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∥a and B∥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 (∥B) dispersive n=0 LL.