We have investigated conduction across electron density discontinuities induced by a front gate on $\frac{\mathrm{GaAs}}{{\mathrm{Al}}_x{\mathrm{Ga}}_{1-x}\mathrm{As}}$ single-interface heterostructures in the integral quantized Hall regime. When the gate is biased so that the Fermi level must cross between adjacent Landau levels at the gate edge, the boundary between higher- and lower-density regions behaves like a backward diode, suggesting the presence in these devices of inter-Landau-level tunneling.

• Received 16 March 1988

DOI:https://doi.org/10.1103/PhysRevLett.61.1123