New selection rules for resonant Raman scattering on quantum wires

¹ Dipartimento di Fisica, INFM, Università di Genova Via Dodecaneso 33, I-16146 Genova, Italy
² I. Institut für Theoretische Physik, Universität Hamburg Jungiusstraße 9, D-20355 Hamburg, Germany

Received: 28 July 1999
Accepted: 15 November 1999

Abstract

The bosonisation technique is used to calculate the resonant Raman spectrum of a quantum wire with two electronic sub-bands occupied. Close to resonance, the cross-section at frequencies in the region of the inter–sub-band transitions shows distinct peaks in parallel polarisation of the incident and scattered light that are signature of collective higher-order spin density excitations. This is in striking contrast to the conventional selection rule for non-resonant Raman scattering according to which spin modes can appear only in perpendicular polarisation. We predict a new selection rule for the excitations observed near resonance, namely that, apart from charge density excitations, only spin modes with positive group velocities can appear as peaks in the spectra in parallel configuration close to resonance. The results are consistent with all of the presently available experimental data.