Quantum antidot as an electrometer: Observation of fractional charge

In experiments on resonant tunneling through a quantum antidot in the quantum Hall (QH) regime, we observe periodic conductance peaks both versus magnetic field and a global gate voltage, i.e., electric field. Each conductance peak can be attributed to tunneling through a quantized antidot-bound state. The fact that the variation of the uniform electric field produces conductance peaks implies that the deficiency of the electrical charge on the antidot is quantized in units of charge of quasiparticles of surrounding QH condensate. The period in magnetic field gives the effective area of the antidot state through which tunneling occurs, the period in electric field (obtained from the global gate voltage) then constitutes a direct measurement of the charge of the tunneling particles. We obtain electron charge 1.57 x 10(-19) C = (0.98 +/- 0.03)e in the integer QH regime, and quasiparticle charge 5.20 x 10(-20) C = (0.325 +/- 0.01)e for the v = 1/3 QH state. (C) 1997 Elsevier Science B.V. All rights reserved.