Spin-polarized two-dimensional electron gas embedded in a semimagnetic quantum well: Ground state, spin responses, spin excitations, and Raman spectrum
Résumé
We present theoretical aspects of spin-polarized two-dimensional electron gas (SP2DEG) which can be achieved in doped semimagnetic quantum wells. This original model system has been recently studied by magneto-Raman-scattering experiments, which has given access to spin-resolved excitations and spectrum of the SP2DEG. Starting from the diluted magnetic semiconductor (DMS) Hamiltonian in the presence of the Coulomb interaction between conduction electrons, we define the conditions to reach such a SP2DEG. The equilibrium state is studied at low temperature; in particular, a theory for the degree of spin polarization is derived. Dynamical spin susceptibilities are further calculated in the framework of a spin-density-functional formalism already developed in the past. We then derive spin-conserving and spin-flip excitation dispersions using a recent determination of the SP2DEG correlation energy corrected from the thickness of the well. The SP2DEG presents two key features: the spin-flip wave, whose existence is a direct consequence of the Coulomb interaction between the spin-polarized electrons with a dispersion and energy range typical of the SP2DEG obtained in DMS, and the spin-density fluctuations exhibiting a specific collective behavior when the spin polarization is increased. The dissipation spectrum through these excitations is studied in detail. Particular attention is given to the spectrum determined by resonant Raman scattering. We show, indeed, that the latter gives unique access to the spin-fluctuation spectrum of the SP2DEG.