Collective electronic excitations in a semiconductor superlattice in the Landau and Wannier-Stark ladder regimeVl. A. Margulis, S. V. Makarov, T. V. Piterimova and E. A. GaidukEur. Phys. J. B, 33 2 (2003) 153-164DOI: https://doi.org/10.1140/epjb/e2003-00152-1