Fractional and unquantized dc voltage generation in THz-driven semiconductor superlatticesK. N. Alekseev, E. H. Cannon, F. V. Kusmartsev and D. K. CampbellEurophys. Lett., 56 6 (2001) 842-848DOI: https://doi.org/10.1209/epl/i2001-00596-9