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

TL;DR

This study reports the observation of a quantum Hall state in CaFeAsF, an iron-based superconductor parent compound, at high magnetic fields, characterized by vanishing conductivities and Landau-level filling factors.

Contribution

It provides experimental evidence for a $ u=0$ quantum Hall state in CaFeAsF, revealing novel high-field magnetotransport phenomena in this material.

Findings

Both conductivities approach zero above 40 T at low temperature.

Landau-level filling factor is $ u=2$ for electrons and holes.

A $ u=0$ quantum Hall state is observed in CaFeAsF.

Abstract

CaFeAsF is an iron-based superconductor parent compound whose Fermi surface is quasi-two dimensional, composed of Dirac-electron and Schr\"odinger-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 $\nu$ = 2 for both electrons and holes at these high field strengths, resulting in a total filling factor $\nu$ = $\nu_{hole} - \nu_{electron}$ = 0. We therefore argue that the $\nu$ = 0 quantum Hall state emerges under these conditions.