New selection rules for resonant Raman scattering on quantum wires

The bosonisation technique is used to calculate the resonant Raman spectrum of a quantum wire with two electronic sub-hands occupied. Close to resonan ce, the cross-section at frequencies in the region of the inter-sub-band tr ansitions shows distinct peaks in parallel polarisation of the incident and scattered light that. are signature of collective higher-order spin densit y excitations. This is in striking contrast to the conventional selection r ule for non-resonant Raman scattering according to which spin modes can app ear only in perpendicular polarisation, We predict a new selection rule for the. excitations observed near resonance, namely that. apart from charge d ensity excitations, only spin modes with positive group velocities can appe ar as peaks in the spectra in parallel configuration close to resonance. Th e results are consistent with all of the presently available experimental d ata.