Bunching of fractionally charged quasiparticles tunnelling through high-potential barriers


Shot noise measurements have been used to measure the charge of quasiparticles in the fractional quantum Hall (FQH) regime1,2,3. To induce shot noise in an otherwise noiseless current of quasiparticles, a barrier is placed in its path to cause weak backscattering. The measured shot noise is proportional to the charge of the quasiparticles; for example, at filling factor v=1/3, noise corresponding to q=e/3 appears. For increasingly opaque barriers, the measured charge increases monotonically, approaching q=e asymptotically4,5. It was therefore believed that only electrons, or alternatively, three bunched quasiparticles, can tunnel through high-potential barriers encountered by a noiseless current of quasiparticles. Here we investigate the interaction of e/3 quasiparticles with a strong barrier in FQH samples and find that bunching of quasiparticles in the strong backscattering limit depends on the average dilution of the quasiparticle current. For a very dilute current, bunching ceases altogether and the transferred charge approaches q=e/3. This surprising result demonstrates that quasiparticles can tunnel individually through high-potential barriers originally thought to be opaque for them.

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Figure 1: Schematic and actual representations of the quasiparticle injector followed by a quasiparticle filter, both made of quantum point contacts, QPC1 and QPC2, respectively.
Figure 3: Comparison of the charge characterizing the pinched QPC2 for two extreme cases of the impinging current: not diluted (noiseless) and highly dilute, keeping the same transmitted current.
Figure 2: Noise and transmission measurements of the pinched QPC2 (with transmission t2 ≈ 0.1 at zero bias) for two different values of dilution of the impinging current: t1=0.7 (a) and 0.2 (b).
Figure 4: Evolution of the effective charge q2 that characterizes the pinched QPC2 in response to different values of dilution t1 of the impinging current (extracted from curves similar to that in Fig. 3a).
Figure 5: Dependence of the transmission t2 of the pinched QPC2 on the dilution t1 of the impinging current.


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The work was partly supported by the Israeli Academy of Science and by the German-Israel Foundation (GIF). We thank A. Yacoby, A. Stern and Y. Levinson for discussions.

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Correspondence to M. Heiblum.

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Comforti, E., Chung, Y., Heiblum, M. et al. Bunching of fractionally charged quasiparticles tunnelling through high-potential barriers. Nature 416, 515–518 (2002). https://doi.org/10.1038/416515a

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