Evidence of superfluidity in double layer 2D electron systems

When two parallel two-dimensional electron gases are sufficiently close together, interlayer Coulomb interactions are of comparable importance to intralayer ones. If the total number of electrons in the bilayer system equals the number of states in the lowest spin-resolved Landau level produced by a large perpendicular magnetic field, an exotic many-body state develops. This state exhibits a variety of remarkable properties including Josephson-like interlayer tunneling and precise quantization of the frictional drag between the layers. These findings lend strong support to the notion that this quantum coherent state is an example of a new kind of superfluid, one in which the underlying bosons are excitons comprised of electrons in one layer bound to holes in the other.