Tunneling Between Two-Dimensional Electron Gases in a Strong Magnetic   Field
  We have measured the tunneling between two two-dimensional electron gases at high magnetic fields $B$, when the carrier densities of the two electron layers are matched. For filling factors $\nu<1$, there is a gap in the current-voltage characteristics centered about $V=0$, followed by a tunneling peak at $\sim 6$~mV. Both features have been observed before and have been attributed to electron-electron interactions within a layer. We have measured high field tunneling peak positions and fitted gap parameters that are proportional to $B$, and independent of the carrier densities of the two layers. This suggests a different origin for the gap to that proposed by current theories, which predict a $\sqrt{B}$ dependence. 
K.M. Brown, N. Turner, J.T. Nicholls, E.H. Linfield, M. Pepper, D.A.   Ritchie, and G.A.C. Jones