Partial hybridisation of electron-hole states in an InAs/GaSb double quantum well heterostructure

InAs/GaSb coupled quantum well heterostructures are important semiconductor systems with applications ranging from spintronics to photonics. Most recently, InAs/GaSb heterostructures have been identified as candidate two-dimensional topological insulators, predicted to exhibit helical edge conduction via fully spin-polarised carriers. We study an InAs/GaSb double quantum well heterostructure with an AlSb barrier to decouple partially the 2D electrons and holes, and find conduction consistent with a 2D hole gas, with an effective mass of 0.235 +/- 0.005 m(0), existing simultaneously with hybridised carriers with an effective mass of 0.070 +/- 0.005 m(0), where m(0) is the bare electron mass.