Transient response of photoexcited electrons with a partially inverted distribution

A nonstationary electron magnetotransport is studied for electrons with a partially inverted distribution formed in the passive region after an ultrashort interband photoexcitation and the emission of a cascade of optical phonons. In the case of a peaked distribution in the passive region, the conductivity is positive because of the greater contribution from the decreasing part of the distribution, while the inverted part of the distribution may give rise to a negative magnetoresistance in classical fields. If the energy of photoexcited electrons in the $c$ zone is a multiple of the optical phonon energy, a pair of half-peaks occurs at the boundaries of the passive region. In this case, the contribution from the inverted part of the distribution (with an energy close to the phonon energy) leads to a total negative conductance and a considerable change in the magnetotransport.