Theory of Two-Dimensional Magnetopolarons

Two-dimensional weak-coupling Fröhlich polarons are investigated theoretically in the presence of an external magnetic field normal to the two-dimensional plane. For a weak magnetic field (${\omega }_c\ll {\omega }_{\mathrm{LO}}$), the cyclotron mass approaches the zero-field polaron effective mass, whereas for large fields (${\omega }_c\gg {\omega }_{\mathrm{LO}}$), the cyclotron mass approaches the bare band mass from below. In the resonance situation (${\omega }_c\approx {\omega }_{\mathrm{LO}}$), the cyclotron mass shows an enhanced polaronic renormalization effect. Connection is made with recent data on magnetoabsorption in semiconductor space-charge layers, explaining why polaron effects show up only in some experiments.