Coupling of lateral and vertical electron motion in GaAs-AlxGa1-xAs quantum wires and dots

Electronic excitations in AlxGa1-xAs-GaAs quantum wires and quantum dots have been investigated by means of resonant inelastic light scattering. At low frequencies, we find quasi-one-dimensional and quasi-zero-dimensional confined plasmons. Interestingly, we observe, at higher frequencies, not only the original two-dimensional (2D) intersubband excitations, but additional modes omega(k) in polarized scattering geometry. The experimental finding is that the frequencies of these modes obey the relation omega(k)(2) approximate to omega(2D)(2)+omega(1D/0D)(2), where omega(2D) is the frequency of the vertical intersubband charge-density excitation. omega(1D) is a lateral quasi-one-dimensional confined plasmon frequency in wires and omega(0D) is the frequency of a quasi-zero-dimensional confined plasmon in dots. This relation shows that the additional modes are collective charge-density excitations, which occur due to a coupling of lateral and vertical electron motion.