A study of the relative strengths of spin-pseudospin phases in a strongly coupled double quantum well system

We perform an experimental and theoretical investigation of the rich phase diagram of quantum Hall paramagnetic and ferromagnetic ground states in a double quantum well (DQW) system, and investigate how the structure of this diagram results from the inter-play between spin and pseudospin exchange energies. We use a comparison with a DQW quantum Hall Hartree calculation to identify the nature of these different phases and assess the effect of exchange and correlation energies. We find that the strengths of different phases and the nature of crossings between them can be understood by the dependence of spin and pseudospin exchange energies on subband wave-function delocalisation which we tune in the DQW system by a surface gate bias.