Abstract:

Using different techniques to individually contact two closely spaced electron gases, we study the tunneling characteristics between weakly coupled GaAs quantum wells, with and without resonant far-infrared excitation. We find that for barriers as thick as 300 a, the alignment between the subbands in the wells can be observed as an increased tunneling conductivity. To study photon-assisted tunneling in our samples, we use the cyclotron resonance as a strong, tunable electronic excitation in the far-infrared. When the Landau-level spacing ?c corresponds to the laser energy ?L, the carriers are effectively pumped to higher Landau levels, which leads to a reduced resistance across the tunnel barrier. This photo-conductive signal is ''doubly resonant'' in that it is at maximum when c coincides with L, and at the same time the subbands of the two wells are aligned.