SPIN-DENSITY AND CHARGE-DENSITY EXCITATIONS IN QUANTUM WIRES

We study an interacting electron gas in a quantum wire within the Hart ree-Fock random-phase approximation. Vertex corrections to the electro n spin polarizability due to the electronic exchange interaction are i mportant giving rise to spin-density excitations (SDE's) with large os cillator strength shifted to lower energies with respect to single-par ticle states. The energy of intersubband SDE's oscillates with the num ber of subbands occupied and has a minimum when a subband energy is cl ose to the chemical potential. Intrasubband SDE's have a linear disper sion at small wave vectors. The corresponding sound velocity is reduce d with respect to the Fermi velocity due to exchange interaction withi n the occupied subbands and exchange screening caused by virtual trans itions to upper subbands. For intersubband and intrasubband charge-den sity excitations (CDE's) vertex corrections are of less importance. Fo r only a single subband occupied the screening of CDE's and SDE's in t he Tomonaga-Luttinger model due to virtual transitions to the upper su bbands is studied, where the virtual transitions are treated within th e Hartree-Fock approximation. The calculations are in good qualitative agreement with experiments.