Tunneling Between Two-Dimensional Electron Gases in a Weak Magnetic Field

We have measured the tunneling between two two-dimensional electron gases (2DEGs) in weak magnetic fields, when the carrier densities of the two electron layers are matched. At zero magnetic field, B = 0, the lineshape of the equilibrium tunneling resonance is best fit by a Lorentzian, with a linewidth which is determined by the roughness of the tunnel barrier. For B 6 = 0 with filling factors ν ≫ 1, there is a suppression of the resonant tunneling conductance about zero bias, V sd = 0. This low field signature of the high field Coulomb gap shows the same linear B dependence as previ-ously measured for ν < 1.