Plasmons in a superlattice with periodic defects

The plasmon excitation spectrum for a multiple-quantum-well superlattice with rectangular defect barriers in each quantum well is calculated in the random-phase approximation. It is demonstrated that both the intersubband and the intrasubband plasma frequencies can be effectively tuned subject to variations of the parameters characterizing the defect barrier in the quantum well, such as the barrier width, its height, and its position in the quantum well. For example, by varying the defect barrier width from 0 to about 40 Å, an order-of-magnitude increase is obtained in the intersubband plasma frequency, with corresponding changes in the intrasubband mode. It is shown that the variations of the collective excitation frequencies follow closely the electron energy subband structures and are therefore equally tunable via the defect barrier.