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We report on our observation of a structure in the valley region of the current-voltage characteristic of a double-barrier resonant-tunneling structure. We attribute this feature to the LOphonon-emission-assisted tunneling of electrons from the emitter electrode to the well. In addition, we observe magnetoquantum oscillations in the valley region, which we interpret as due to a momentum-nonconserving component of the tunneling current.

We have studied nonlocal electrical transport over macroscopic distances in the regime of the fractional quantum Hall effect (FQHE). Experiments clearly demonstrate dissipationless edge-state conduction associated with the FQHE. Surprisingly, our data imply that there is no edge-state conduction near filling factor v= j and on the low-v side of the v = 1 QHE state, while edge-state conduction is observed near v= f and on the high-v side of the v = l QHE state. We also observe that the electron-hole symmetry is broken for the edge states in a confined geometry.

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