Magnetic dipole absorption of light at intersubband transitions in quantum wells

We consider theoretically the magnetic dipole mechanism of IR-light absorption at intersubband transitions in wide-gap quantum wells (QWs). In contrast to the electric dipole resonance, the discussed mechanism manifests in the interaction with the s-polarized component of electromagnetic radiation. We demonstrated that (a) the frequencies of magnetic and electric dipole intersubband transitions in the 2D layer are equal in the framework of one-particle approximation; (b) collective plasma effects should lead to a significant frequency shift between the magnetic and electric dipole resonances in a typical QW. Consequently, independent measurements of the magnetic and electric dipole resonant frequencies could allow both the extraction of the QW parameters and the experimental verification of theoretical models of collective fermion interaction. Taking into account the relative weakness of the magnetic dipole absorption, we propose a waveguide scheme for its experimental observation.