Regensburg 2004 – wissenschaftliches Programm
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TT: Tiefe Temperaturen
TT 3: Spin-Systeme und itinerante Magnete
TT 3.4: Vortrag
Montag, 8. März 2004, 10:15–10:30, H18
Theory of spin waves in diluted-magnetic-semiconductor quantum wells — •Diego Frustaglia1,2, Jürgen König3,2, and Allan MacDonald4 — 1Scuola Normale Superiore, Pisa, Italy — 2Institut für Theoretische Festkörperphysik, Universität Karlsruhe, Germany — 3Institut für Theoretische Physik III, Ruhr-Universität Bochum, Germany — 4Department of Physics, University of Texas, Austin, USA
We present a theory of collective spin excitations in diluted magnetic semiconductor quantum wells, in which local magnetic moments are magnetically coupled via a quasi-two-dimensional electron or hole gas. In contrast to bulk systems, a multiplet of spin-wave branches is predicted. We discuss the dispersion of these collective excitations and the profiles of the corresponding modes for different magnetic-ion doping concentrations and free-carrier densities. In the case of a ferromagnetic state with a partially spin-polarized two-dimensional electron gas, we find that the Goldstone collective mode has anomalous k4 dispersion and that for symmetric quantum wells odd parity modes do not disperse at all. Moreover, we further discuss the gap in the collective excitation spectrum which appears when spin-orbit interactions are included.