Physical Review B
The American Physical Society
We present a phenomenological picture for the many-body excitations of a two-dimensional electron gas in a quantum well spin polarized by a dc magnetic ﬁeld at an angle with the axis of the well. In the framework of the Landau theory of charged Fermi liquids, we determine the frequencies of collective modes by solving a transport equation for quasiparticles in the local electromagnetic ﬁeld associated with the charge- and spin-density ﬂuctuations. In the long-wavelength limit, analytic solutions for (qជ) are obtained as functions of the degree of spin polarization and of the angle .
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