Resonant Magneto-optical Transitions from a Mid-Gap Level inn-InSb

The first magneto-optical transitions originating from a deep defect level in high-purity $n$-InSb are observed in the C${\mathrm{O}}_2$-laser-induced resonant photoconductivity at low magnetic fields. Another series of resonant structures is associated with three-LO-phonon-assisted spin-conserving cyclotron harmonic transitions.