Inelastic light scattering by spin-density, charge-density, and single-particle excitations in GaAs quantum wires

We report the observations of inelastic light scattering by the elementary excitations of the one-dimensional electron gas. The quantum wires are fabricated from a modulation-doped single GaAs/${\mathrm{Al}}_{\mathit{x}}$ ${\mathrm{Ga}}_{1\mathrm{-}\mathit{x}}$As quantum well electron-beam lithography and shallow electron-cyclotron-resonance reactive-ion etching. In spectra of intersubband excitations we observe a clear separation of spin-density and charge-density collective modes. The splitting associated with the lateral potential of the wires is also seen in transitions to states of the first excited level of the parent quantum well. Determinations of electron-electron interactions in intersubband excitations of the one-dimensional electron gas show large corrections due to the exchange terms (or vertex corrections) that represent the excitonic binding of the particle-hole pairs.