Collective nature of two-dimensional electron gas spin excitations revealed by exchange interaction with magnetic ions

Time-resolved Kerr rotation experiments in CdMnTe quantum wells provide the evidence of mixed spin excitations of the two-dimensional electron gas and magnetic ions. The onset of strong coupling between electron and Mn spin modes reveals the collective (spin-wave) nature of electronic spin excitations probed by this method. We show that resonant exchange coupling between electron-spin waves and magnetic ions spin-flip excitations provide insights in the many-body physics of the two-dimensional electron gas.