Transport in β-Bi₄I₄ beyond the quantum limit
Low-field oscillations measured the cyclotron mass; transport at much higher fields showed evidence of a gap.
Peng Wang, Liyuan Zhang and colleagues first measured quantum oscillations in β-Bi₄I₄ single crystals at low temperatures. They inferred a cyclotron mass of about one tenth of the free-electron mass and used field rotation to probe the shape of the associated Fermi surface.
After the field drove the carriers into their lowest Landau level, the sample underwent a metal–insulator transition. Farther beyond the quantum limit, the temperature dependence of resistance indicated a field-induced gap, consistent with magnetic freeze-out.