Observation of quasiparticles with one-fifth of an electron's charge

The fractional quantum Hall effect(1) occurs in the conduction properties of a two-dimensional electron gas subjected to a strong perpendicular magnetic field. In this regime, the Hall conductance shows plateaux, or fractional states, at rational fractional multiples of e(2)/h, where e is the charge of an electron and h is Planck's constant. The explanation(1-3) of this behaviour invokes strong Coulomb interactions among the electrons that give rise to fractionally charged quasiparticles which can be regarded as noninteracting current carriers(1-5). Previous studies(4,5) have demonstrated the existence of quasiparticles with one-third of an electron's charge, the same fraction as that of the respective fractional state. An outstanding ambiguity is therefore whether these studies measured the charge or the conductance. Here we report the observation of quasiparticles with a charge of e/5 in the 2/5 fractional state, from measurements of shot noise in a two-dimensional electron gas(4.) Our results imply that charge can be measured independently of conductance in the h factional quantum Hall regime, generalizing previous observations of fractionally charged quasiparticles.