Collective Modes of an Electron-Hole System in a Magnetic Field. III

Abstract

The dependence of the charge-density waves on a propagation direction is investigated in a long-wavelength limit. It is shown that there exists a characteristic magnetic field H₀ at which electrons and holes oscillate with the non-magnetic plasma frequency \sqrtω_p^e2+ω_p^h2 for an arbitrary direction of propagation. This field is determined by electron and hole masses, carrier concentrations and a dielectric constant of the medium. For a perpendicular propagation to this field H₀, the highest frequency of the three collective modes is given by \sqrtω_c^e2+ω_c^h2 with out-of-phase oscillation of electrons and holes. The polarization property and the dispersion relation of the modes are investigated.