The ultra-quantum limit is achieved when a magnetic field confines an electron gas in its lowest spin-polarised Landau level. Here we show that in this limit, electron doped ZrTe5 shows a metal-insulator transition followed by a sign change of the Hall and Seebeck effects at low temperature. We attribute this transition to a magnetic freeze-out of charge carriers on the ionised impurities. The reduction of the charge carrier density gives way to an anomalous Hall response of the spin-polarised electrons. This behaviour, at odds with the usual magnetic freeze-out scenario, occurs in this Dirac metal because of its tiny Fermi energy, extremely narrow band gap and a large g-factor. We discuss the different possible sources (intrinsic or extrinsic) for this anomalous Hall contribution.
@article{arxiv.2205.01622,
title = {Magnetic freeze-out and anomalous Hall effect in ZrTe$_5$},
author = {Adrien Gourgout and Maxime Leroux and Jean-Loup Smirr and Maxime Massoudzadegan and Ricardo P. S. M. Lobo and David Vignolles and Cyril Proust and Helmuth Berger and Qiang Li and Genga Gu and Christopher C. Homes and Ana Akrap and Benoît Fauqué},
journal= {arXiv preprint arXiv:2205.01622},
year = {2022}
}