Magnetoexciton Superfluidity in Graphene-Dielectric-Graphene Structures

Abstract

Superfluid state of a magnetoexciton gas in bilayers is studied with reference to graphene-dielectric-graphene structures subjected by a perpendicular to graphene layers magnetic field B. We find that in difference with quantum Hall bilayers with the total filling factor vT = 1, an imbalance of filling factors of graphene layers is required. An imbalance can be created by an electrostatic field E applied perpendicular to graphene layers. We determine the range of B and E where magnetoexciton superfluidity can be realized. The dependence of critical temperature and critical current on magnetic field is computed. It is found that the maximum critical temperature is reached at B ≍ 0.5ø0ød2, where ø0 is the magnetic flux quantum, and d is the interlayer distance. It is shown that the interaction of electrons with impurities reduces the critical temperature. The critical concentration of impurities is determined. Stationary waves in a superfluid magnetoexciton gas are considered. The waves are induced by counter-propagating electrical currents that flow in a bilayer with a point obstacle. It is found that the stationary wave pattern is modified qualitatively under variation of B.