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Direct observation of a fractional charge


Since Millikan's famous oil-drop experiments1, it has been well known that electrical charge is quantized in units of the charge of an electron, e. For this reason, the theoretical prediction2,3 by Laughlin of the existence of fractionally charged ‘quasiparticles’—proposed as an explanation for the fractional quantum Hall (FQH) effect—is very counterintuitive. The FQH effect is a phenomenon observed in the conduction properties of a two-dimensional electron gas subjected to a strong perpendicular magnetic field. This effect results from the strong interaction between electrons, brought about by the magnetic field, giving rise to the aforementioned fractionally charged quasiparticles which carry the current. Here we report the direct observation of these counterintuitive entities by using measurements of quantum shot noise. Quantum shot noise results from the discreteness of the current-carrying charges and so is proportional to both the charge of the quasiparticles and the average current. Our measurements of quantum shot noise show unambiguously that current in a two-dimensional electron gas in the FQH regime is carried by fractional charges—e/3 in the present case—in agreement with Laughlin's prediction.

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Figure 1: The total current noise inferred to the input of the preamplifier as a function of the input conductance at equilibrium (circles).
Figure 2: Quantum shot noise as a function of direct current, I, through the QPC without an applied magnetic field (circles).
Figure 3: Quantum shot noise as a function of the backscattered current, IB, in the FQH regime at ν = 1/3 for two different transmission coefficients through the QPC (circles and squares).
Figure 4


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The work was partly supported by a grant from the Israeli Science Foundation and by a grant from the Austrian Ministry of Science.

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Correspondence to R. de-Picciotto.

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de-Picciotto, R., Reznikov, M., Heiblum, M. et al. Direct observation of a fractional charge. Nature 389, 162–164 (1997).

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