Plasma Oscillations in a Superlattice

Tho spectrum of plasma oscillations, propagating along the superlattice (SL) axis is calculated in the random phase approximation (RPA) taking the umklapp processes into account. In the case of strong screening the plasmon frequency is determined by SL parameters and temperature and found to do not depend on wave number. At weak screening quasineutral electron oscillations occur. In the case of small wave numbers the oscillations follow the acoustic law of dispersion and propagate with a frequency of the same order as the electronic ones along the SL axis. The characteristic feature of plasmons propagating along the SL axis, is the absence of Landau damping since the decay of these plasmons in pairs of quasi‐particles is forbidden by energy‐momentum conservation laws. The existence of plasmons, propagating along the axis, may be an indication of electron tunnelling between layers.