Novel electron gas systems

We review recent progress on the physics of electrons in the bilayered elec tron gas, relevant to coupled quantum wells in GaAs/AlGaAs heterostructures . First, we focus on the phase diagram of a symmetric bilayer at T = B = 0, obtained by diffusion Monte Carlo simulations. It is found that inter-laye r correlations stabilize crystalline structures at intermediate inter-layer separation, while favouring a liquid phase at smaller distance. Also, the available DMC evidence is in contrast with the recently (Hartree-Fock) pred icted total charge transfer (TCT), whereby all the electron spontaneously j ump in one layer. In fact, one can show that such a TCT state is never stab le in the ideal bilayer with no tunneling. We finally comment on ongoing DM C investigations on the electron-hole bilayer, where excitonic condensation is expected to take place.