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

The fractional quantum Hall effect(1) occurs in the conduction properties o f a two-dimensional electron gas subjected to a strong perpendicular magnet ic field. In this regime, the Hall conductance shows plateaux, or fractiona l 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 be haviour invokes strong Coulomb interactions among the electrons that give r ise to fractionally charged quasiparticles which can be regarded as noninte racting current carriers(1-5). Previous studies(4,5) have demonstrated the existence of quasiparticles with one-third of an electron's charge, the sam e fraction as that of the respective fractional state. An outstanding ambig uity is therefore whether these studies measured the charge or the conducta nce. 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-dimen sional electron gas(4.) Our results imply that charge can be measured indep endently of conductance in the h factional quantum Hall regime, generalizin g previous observations of fractionally charged quasiparticles.