Resistance fluctuations in the integral- and fractional-quantum-Hall-effect regimes

We report on our measurements of resistance fluctuations as a function of magnetic field B in an AlxGa1-xAs/GaAs heterostructure of etched width w=2.5 m in the integral- and fractional-quantum-Hall-effect regimes. High-frequency fluctuations are observed near the longitudinal resistance (Rxx) minima for =1, 2, 3, 4, and 1/3. The quasiperiods B( = integer) of the fluctuations for integer are all 0.016 T, while for =1/3, the quasiperiod B( = 1/3) is 0.05 T, or a factor of 3 larger. The fluctuations at integer are consistent with inter-edge-state tunneling via magnetically bound states encircling a potential hill of a diameter roughly equal to the conducting width of the channel. A similar model, with the difference that the tunneling is by quasiparticles of fractional charge e*=e/q, predicts a scaling of the quasiperiod as B(=1/q)=q B( = integer). Interpreted in terms of this model, the data provide direct evidence of the existence of quasiparticles of charge e*=e/3 in the =1/3 fractional quantum Hall effect. For both =1/3 and = integer, the individual fluctuation patterns for different pairs of voltage probes are strongly correlated only if the pairs share a length of the channel, indicating that the source of the fluctuations is local, as predicted by the model. A Coulomb blockade as the origin of the fluctuations is ruled out by the fact that for =1 and 2 the fluctuation amplitudes saturate at temperatures Tc(=1)66 mK and Tc(=2)121 mK, and also saturate at currents Ic(=1)0.5 nA and Ic(=2)1.73.0 nA. These results indicate that for integer, the bound-state-energy spacing () scales as or B-1, inconsistent with a Coulomb blockade.