Theory of Cyclotron Resonance of Fröhlich Polarons in High Magnetic Fields

Abstract

Cyclotron resonance of polarons in ionic crystals is studied by means of a Born‐Oppenheimer type method. The Lee, Low, Pines approximation is made for the electron—phonon interaction and so the translational invariance along the magnetic field direction is exploited. Our approach is therefore valid at weak and intermediate couplings and cyclotron frequencies ω_c larger than the L.O. phonon frequency ω, which requires rather intense magnetic fields. For relatively large electron—phonon coupling (α ≧ 4) the results also apply qualitatively for weak magnetic fields. The ground state energy and the energy of two excited levels are obtained. The excited states which are treated here are internal excited states of the polaron system and they are different from the normal Landau levels. The stability of some of these states is enhanced under the action of the magnetic field. This leads us to predict absorption at new cyclotron frequencies in ionic crystals especially relevant for intermediate coupling strengths α ≈ 4.