Large splitting of the cyclotron Resonance line in AlxGa1-XN/GaN heterostructures

Cyclotron-resonance (CR) measurements on two-dimensional (2D) electrons in AlGaN/GaN heterojunctions reveal large splittings (up to 2 meV) of the CR line for all investigated densities, n sub 2D, from 1 to 4x10 sup 12 cm sup -2 over wide ranges of a magnetic field. The features resemble a level anti-crossing and imply a strong interaction with an unknown excitation of the solid. The critical energy of the splitting varies from 5 to 12 meV and as the square root of n sub 2D. The phenomenon resembles data from AlGaAs/GaAs whose origin remains unresolved. It highlights a lack of basic understanding of a very elementary resonance in solids.