Direct observation of a fractional charge

Abstract

Ever since Millikan’s [1]famous experiment it is well known that the electrical charge is quantized in units of the electronic charge – e. For that reason, Laughlin’s [2, 3]theoretical prediction of the existence of fractionally charged quasi-particles, put forward in order to explain the fractional quantum Hall (FQH) effect, is very counter intuitive. The FQH effect is a phenomenon that occurs in a two-dimensional electron gas (2DEG) subjected to a strong perpendicular magnetic field. This effect results from the strong interaction among the electrons and consequently current is carried by the above-mentioned quasi-particles. We directly observed this elusive fractional charge by utilizing a measurement of quantum shot noise. Quantum shot noise results from the discreteness of the current carrying charges and thus is proportional to their charge, Q, and to the average current I, namely, S i =2 QI Our quantum shot noise measurements unambiguously show that current in a 2DEG in the FQH regime, at a fractional filling factor ν= 1 3 , is carried by fractional charge portions e/3; in agreement with Laughlin’s prediction.