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Title: Origin of Hall plateaus in bulk ZrTe5
Plain: Thick crystals of ZrTe5 show Hall-resistance plateaus resembling the quantum Hall effect, which normally needs a two-dimensional sample, and whether a field-induced charge-density wave causes them is unsettled.
Precise: In bulk ZrTe5 (and HfTe5), Tang et al. (Nature, 2019) reported Hall plateaus with $\rho_{xy}\sim (1/2)(h/e^2)\lambda_z$, $\lambda_z$ the Fermi wavelength along the field, attributed to a field-induced charge-density wave in the quantum limit. Determine whether a density modulation and gap exist or whether the plateau-like features come from quantum-limit band physics alone. An answer is an identification backed by direct structural or spectroscopic evidence.
Settled by: X-ray diffraction or ultrasound in the quantum limit detecting or excluding a density modulation with wavelength $\sim \lambda_z/2$, with transport on the same samples.
Kind: well-posed
Answer type: identification
References: (empty)
Literature status: contested
Status note: Thermodynamic and transport studies from 2021 argued the plateaus arise without a charge-density wave; no direct structural detection as of 2026.
Posed since: 2019