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Anomalous High-Field Magnetotransport in CaFeAsF due to the Quantum Hall Effect

CaFeAsF is an iron-based superconductor parent compound whose Fermi surface is quasi-two dimensional, composed of Dirac-electron and Schrödinger-hole cylinders elongated along the $c$ axis. We measured the longitudinal and Hall resistivities in CaFeAsF with the electrical current in the $ab$ plane in magnetic fields up to 45 T applied along the $c$ axis and obtained the corresponding conductivities via tensor inversion. We found that both the longitudinal and Hall conductivities approached zero above $\sim$40 T as the temperature was lowered to 0.4 K. Our analysis indicates that the Landau-level filling factor is $ν$ = 2 for both electrons and holes at these high field strengths, resulting in a total filling factor $ν$ = $ν_{hole} - ν_{electron}$ = 0. We therefore argue that the $ν$ = 0 quantum Hall state emerges under these conditions.