Current–voltage characteristics of GaAs/AlAs superlattices have been measured using long-pulsed magnetic fields up to 37 T applied parallel to the growth axis. In the region of Wannier–Stark localisation a combined Wannier–Stark Landau ladder of states is obtained and a number of resonant features corresponding to inter-well transitions are observed. At low magnetic fields, their voltage positions increase with magnetic field. However at magnetic fields above about 18 T, their voltage positions become independent of magnetic field owing to a pinning effect associated with polaronic coupling to the longitudinal-optic phonon mode.
Hayden, RK., Nogaret, A., Eaves, L., Miura, N., & Henini, M. (1998). Polaron pinning effects in superlattices at high electric and magnetic fields. Physica B: Condensed Matter, 256 - 258, 540-543. https://doi.org/10.1016/S0921-4526(98)00536-5