Experimental determination of the quasiparticle charge and the energy gap in the fractional quantum Hall effect

We have studied the energy gap in the 1/3-filling fractional quantum Hall effect state in GaAs/AlxGa1-xAs heterojunctions with a carrier concentration tuned by a gate voltage. We have measured in situ (i) a fractional signature in a capacitance between a two-dimensional electron system and a metal gate, and (ii) the activation energy of magnetoresistance. From the capacitance data, using recently proposed assumptions, we have evaluated the chemical potential discontinuity in the 1/3-filling state. It turned out to be in good agreement with a value expected from the measured activation energy under the assumption of the fractional quasiparticle charge e*=±e/3. This result suggests that the approach used can be employed to determine absolute values of both the energy gap and the fractional quasiparticle charge.