Effect of disorder on superfluidity in double layer graphene

Abstract

Post-CMOS logic in bilayer graphene is very promising due to the possibility of observing room temperature collective states. An excitonic superfluid is predicted to form in double layer graphene systems at room temperature if the two individual monolayers of graphene are separated by an oxide no more than a few nanometers thick [1]. Recent experiments have shown evidence of interaction enhanced transport in double layer graphene [2], but there is a significant discrepancy in the quality of the two graphene layers which may be occluding the phase transition. We present and compare the performance characteristics of ideal and disordered double layer graphene systems at room temperature in the purported regime of superfluidity. We perform quantum transport calculations on double layer graphene using the Non-Equilibrium Green's Function (NEGF) formalism in an effort to elucidate the evolution of a BEC under non-equilibrium conditions in the presence of lattice defects. We find that lattice defects spread throughout the channel can degrade interlayer current by 30%, but disorder concentrated near the contacts causes a much more significant reduction of 80% in interlayer current. We also find that steady-state spontaneous coherence is lost for defect concentrations greater than 4%; a very clean system is therefore necessary for potential post-CMOS logic applications.