Minigaps and Novel Giant Negative Magnetoresistance in InAs/GaSb Semimetallic Superlattices

The magnetoresistance of semimetallic InAs/GaSb superlattices has been measured in parallel magnetic fields. The temperature dependence reveals for the first time the existence of a minigap at the anticrossing points between the electron and hole dispersion relations. At high magnetic fields, samples which are close to intrinsic show surprisingly large decreases in resistance of up to 70%. The magnetoresistance also depends on crystal orientation. We present a theoretical model which explains the experimental observations and estimates the minigap to be of order 7 meV.