Interacting Intersubband Excitations in Parabolic Semiconductor Quantum Wells

摘要

We calculate the finite wave-vector intersubband collective excitation in spectrawide parabolic wells at low two-dimensional electron densities where only the lowest quantum subband is occupied by electrons. We use a self-consistent time-dependent local-density approximation to calculate the linear response of the system, comparing our density functional results with the noninteracting time-dependent Hartree approximation to estimate the magnitudes of exchange-correlation correction to the collection-mode dispersion. We predict a qualitatively new phenomenon at low electron densities where, in the presence of exchange-correlation effects, it becomes possibly for the collective charge-density excitation (i.e., the intersubband plasmon mode) to lie below the intersubband quasiparticle continuum. As the electron density is lowered, the charge-density excitation passes through the intersubband single-particle Landau continuum, eventually going below the intersubband single-particle excitations.