Bunching of Fractionally-Charged Quasiparticles Tunneling through High Potential Barriers

Shot noise measurements were recently exploited to measure the charge of the quasiparticles in the Fractional Quantum Hall (FQH) regime. For fractional filling factors nu=1/3 and 2/5 of the first Landau level, fractional charges q=e/3 and e/5, respectively, were measured. We investigate here the interaction of e/3 quasiparticles with a strong backscatterer and find unexpected results. When a weak backscatterer is introduced in the path of an otherwise noiseless current of quasiparticles, stochastic partitioning of the quasiparticles takes place and shot noise proportional to their charge appears. Specifically, at nu=1/3, noise corresponding to q=e/3 appears. However, the measured charge increases monotonically as backscattering becomes stronger, approaching asymptotically q=e. In other words, only electrons, or alternatively, three bunched quasiparticles, tunnel through high potential barriers when impinged by a noiseless current of quasiparticles. Here we show that such bunching of quasiparticles by a strong backscatterer depends on the average occupation (dilution) of the impinging quasiparticle current. For a very dilute impinging current, bunching ceases altogether and the transferred charge approaches q=e/3. These surprising results prove that a sparse beam of quasiparticles, each with charge e/3, tunnel through high potential barriers, originally thought to be opaque for them.