Collective excitations in an asymmetrically spin-polarized quantum well

We present a phenomenological picture for the many-body excitations of a tw o-dimensional electron gas in a quantum well spin polarized by a de magneti c field at an angle theta with the axis of the well. In the framework of th e Landau theory of charged Fermi liquids, we determine the frequencies of c ollective modes by solving a transport equation for quasiparticles in the l ocal electromagnetic held associated with the charge- and spin-density fluc tuations. In the long-wavelength limit, analytic solutions for omega((q) ov er right arrow) are obtained as functions of the degree of spin polarizatio n and of the angle theta. [S0163-1829(98)06144-X].