Collective intersubband spin- and charge-density excitations in tilted magnetic fields

Collective intersubband excitations, from the ground to the first excited electronic subband, are studied via inelastic light scattering in modulation-doped GaAs/${\mathrm{Al}}_{\mathit{x}}$${\mathrm{Ga}}_{1\mathrm{-}\mathit{x}}$As quantum wells. The application of a magnetic field, tilted with respect to the growth direction, allows coupling of electron motion in the plane of the quantum well to motion along the growth axis such that combined intersubband–cyclotron-resonance transitions are observed. Anticrossing behavior between the combined resonances and the collective charge- or spin-density excitations is exhibited in the polarized or depolarized Raman-scattering geometries, respectively. The combined resonances show weak collective effects allowing an extrapolation of the bare subband separation and hence measurements of the depolarization and exchange-correlation shifts. Comparison to a theory employing the local-density approximation yields excellent results.