Tight-binding study of electron-hole pair condensation in graphene bilayers: Gate control and system-parameter dependence

The theoretical prediction of high-temperature electron-hole pair condensation when two graphene layers are separated by a thin dielectric film has motivated experimental work which aims to observe this condensate, and theoretical work which explores how its collective behavior could be used to design beyond-CMOS low-power electronic logic devices. Here we use a pi-band tight binding model combined with Fock mean-field theory to explore the condensate properties. We study the effects of charge density, dielectric permittivity, interlayer separation, and temperature, on the formation and strength of the condensate. We model the weakening and eventual collapse of the condensate with increasing charge imbalance between layers, a mechanism which has been proposed for beyond-CMOS switching based on condensate control. Finally, we explore critical currents in the weak-coupling limit. We demonstrate that the critical current is extremely sensitive to the strength and character of interlayer tunneling processes, especially when these are weak.