Evidence for an interlayer exciton in tunneling between two-dimensional electron systems

Experiments on the tunneling of electrons between parallel two-dimensional systems at high magnetic field present strong evidence for a final state excitonic attraction between a tunneled electron and the hole it leaves behind. This evidence is obtained from the observed dependences of the tunneling spectra upon the thickness of the separating barrier and the densities of the electron gases. We suggest that both two dimensionality and confinement to the lowest Landau level greatly enhance the importance of this unusual exciton.