We analyze the high-frequency dynamic conductivity of a tunneling GaAs/${\mathrm{Al}}_{\mathrm{x}}$${\mathrm{Ga}}_{1\mathrm{-}\mathrm{x}}$As superlattice using the memory-function technique. Considering relatively small wave-function overlap between adjacent quantum wells in the tight-binding approximation, we examine the plasmon resonance structure of the ac conductivity for transport parallel to the quantum-well planes. Employing the random-phase-approximation density-density correlation function for a tunneling superlattice, we find that the imaginary part of the memory function continuously increases to its maximum and then gradually decreases in the region ${\omega }_p$∼3${\omega }_p$. The shift of the peak of Im[M(ω)] above ${\omega }_p$ may be attributed to a nonlocal dispersive shift of the close-packed tunneling superlattice plasmon, and the peak is seen to decrease as barrier height decreases in a way that is consonant with relatively small plasmon-pole conductivity contribution in the three-dimensional bulk case.

• Received 26 September 1989

DOI:https://doi.org/10.1103/PhysRevB.41.2966