Nature
Three-dimensional quantum Hall effect and metal–insulator transition in ZrTe₅
Nature · 569, 537-541 (2019)
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Introduction
A magnetic field drove bulk ZrTe₅ into the lowest Landau level. At low temperature the longitudinal resistivity approached zero while the Hall resistivity formed a plateau. Its height scaled with half the Fermi wavelength along the field, which the authors interpreted as evidence for a three-dimensional quantum Hall state. At higher field they observed a metal–insulator transition.
A closer reading
A bulk Hall resistivity carries a length dimension that a two-dimensional sheet resistance does not. Here that length is tied to the Fermi surface. Reading the scaling together with the low longitudinal dissipation makes the argument more informative than the plateau shape alone. The proposed interaction-driven instability is a microscopic interpretation of those measurements.