COLLECTIVE INTERSUBBAND SPIN-DENSITY EXCITATIONS IN A QUANTUM-WIRE INA MAGNETIC-FIELD

We study an interacting electron gas parabolically confined to a quant um wire in a perpendicular magnetic field. We consider the case of mor e than one subband occupied in the ground state. The intersubband spin -density excitations are calculated within the Hartree-Fock random-pha se approximation. Similarly to the case in the absence of a magnetic f ield, vertex corrections to the electron spin polarizability are impor tant, leading to collective spin-density excitations red-shifted with respect to the Hartree-Fock single-particle energies. In a finite magn etic field, the triplet of spin-density excitations splits. The splitt ing is at its maximum if the chemical potential is in between the bott om of a spin-up subband and the bottom of a spin-down subband, when th e g-factor is greatly enhanced due to the exchange interaction.