QUANTUM-THEORY OF PLASMONS IN LATERAL MULTIWIRE SUPERLATTICES - INTRASUBBAND PLASMONS AND THEIR COUPLING TO INTERSUBBAND PLASMONS

We analyze intrasubband plasmons in lateral multiwire superlattices and study their coupling to intersubband plasmons. We find that the local approximation is equivalent to neglecting the umklapp contributions to the plasmon energy. While this approximation fails completely for intersubband plasmons, it is reasonable for intrasubband plasmons in the long-wavelength limit. In common with intersubband plasmons, an approximate sum rule exists for intrasubband plasmons, but unlike the case for intersubband plasmons, here it is more precise because it tends to be independent of the details of the confining potential. It is predicted that in a system with n populated subbands, we should observe experimentally only one intrasubband plasmon mode. For zero wave vector along the superlattice direction, intrasubband plasmons only couple to even-parity intersubband plasmons. The coupling of intrasubband plasmons to the dominant intersubband plasmons and other odd-parity intersubband plasmons is very weak in general. Experiments are proposed to verify the importance of Coulomb coupling between wires.