Interplay of quasi-quantum Hall effect and Coulomb disorder in semimetals

Abstract Low carrier densities in semimetals enable the exploration of magnetotransport in the quantum limit. Recent findings consistent with 3D quasi-quantum Hall effect (QQHE) have positioned semimetals as promising platforms for exploring 3D quantum Hall-like transport, but the lack of tunability in the Fermi level has limited QQHE observation. Here, we show how achieving ultralow carrier densities in the Dirac semimetal Cd 3 As 2 ( ~ 10 16 cm −3 ) can reveal QQHE signals at modest fields. At these low densities where QQHE is most accessible, we find that clear QQHE is obscured by charged disorder, which broadens Landau bands, scatters carriers, and affects quasi-quantization. Clear observation of QQHE in semimetals depends on Fermi level and disorder potential magnitudes. As theoretically predicted, Coulomb disorder is an essential ingredient for understanding the magnetoresistivity for a spectrum of Fermi levels in Cd 3 As 2 , anchoring the role of charged disorder in topological semimetal applications. We discuss future constraints and opportunities in exploring 3D QQHE in semimetals.