Bunching of Fractionally-Charged Quasiparticles Tunneling through High Potential Barriers

摘要

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