7 research outputs found
Graphene Bilayer Structures with Superfluid Magnetoexcitons
We study superfluid behavior of a gas of spatially indirect magnetoexcitons
with reference to a system of two graphene layers embedded in a multilayer
dielectric structure. The system is considered as an alternative of a double
quantum well in a GaAs haterostructure. We determine a range of parameters
(interlayer distance, dielectric constant, magnetic field and gate voltage)
where magnetoexciton superfluidity can be achieved. Temperature of superfluid
transition is computed. A reduction of critical parameters caused by impurities
is evaluated and critical impurity concentration is determined
Exciton Condensation and Perfect Coulomb Drag
Coulomb drag is a process whereby the repulsive interactions between
electrons in spatially separated conductors enable a current flowing in one of
the conductors to induce a voltage drop in the other. If the second conductor
is part of a closed circuit, a net current will flow in that circuit. The drag
current is typically much smaller than the drive current owing to the heavy
screening of the Coulomb interaction. There are, however, rare situations in
which strong electronic correlations exist between the two conductors. For
example, bilayer two-dimensional electron systems can support an exciton
condensate consisting of electrons in one layer tightly bound to holes in the
other. One thus expects "perfect" drag; a transport current of electrons driven
through one layer is accompanied by an equal one of holes in the other. (The
electrical currents are therefore opposite in sign.) Here we demonstrate just
this effect, taking care to ensure that the electron-hole pairs dominate the
transport and that tunneling of charge between the layers is negligible.Comment: 12 pages, 4 figure