Exchange interaction effects in electron spin resonance: Larmor theorem violation in narrow-gap quantum well heterostructures.

We report a theoretical study of the exchange interaction effects in the electron spin resonance (ESR) in n-type narrow-gap quantum well (QW) heterostructures. Using the Hartree-Fock approximation, based on the eight-band k⋅p Hamiltonian, the many-body correction to the ESR energy is found to be nonzero, providing theoretical evidence of Larmor theorem violation in symmetric narrow-gap QWs. We predict the exchange enhancement of the ESR g-factor and its divergence in low magnetic fields. The 'enhanced' ESR g-factor and quasiparticle g-factor, measured in magnetotransport, coincide at even-valued filling factors of the Landau levels in moderate and quantizing magnetic fields.