Optical probing of the minigap in InAs/GaSb superlattices

We report strong modulations in the far infrared absorption of InAs/GaSb semimetallic superlattices under the influence of a parallel magnetic field and attribute this to direct transitions across the minigap. The experiments have been performed on a variety of structures with the measured minigap energies in the range 3–23 meV. For narrow layered samples where the two band picture is valid a broad minigap absorption is observed. On increasing the well and barrier widths the absorption decreases in energy and also becomes more localized as more bands anticross to form multiple minigaps. The results are compared with parallel field magnetoresistance experiments as well as eight band $\mathbf{k}\cdot \mathbf{p}$ theory.