Origin of Hall plateaus in bulk $\mathrm{ZrTe_5}$

In bulk $\mathrm{ZrTe_5}$ (and $\mathrm{HfTe_5}$), 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.

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.