Collective excitation in ${\mathrm{G}\mathrm{a}\mathrm{A}\mathrm{s}-\mathrm{A}\mathrm{l}}_x{\mathrm{Ga}}_{1-x}$As quantum wires: Multisubband model

The effects of the potential barrier height on the collective excitations of an electron gas confined in a GaAs-Al${}_x$Ga${}_{1-x}$As quantum wire of rectangular cross section are investigated theoretically by using the self-consistent field approximation theory proposed by Singwi, Tosi, Land, and Sjölander (STLS) [Phys. Rev. 176, 589 (1968)]. For several potential barrier heights, we calculated the effective potential, plasmon energy, structure factor, and pair-correlation function, considering a three-subband model with only the lowest subband populated by electrons. We verified that the intersubband plasmon is more sensitive to the potential barrier height variation than the intrasubband plasmon. We also observed that the confining potential effect decreases with the increasing of the wire width. The random-phase approximation results are also presented by comparison with the STLS results and significant differences were found.