Researchers have directly measured the electrical charges of fractionally charged quasiparticles using a gate-defined bilayer-graphene antidot, according to a study published in Nature Physics. The device operated in the Coulomb-dominated regime to evaluate quasiparticle tunnelling across both integer and fractional quantum Hall states.
The team fabricated the antidot by etching a 300-nanometre hole into a top graphite gate placed over hexagonal boron nitride-encapsulated bilayer graphene. Side gates adjusted edge channel transmission through the constriction, while top and bottom graphite gates controlled local carrier densities and external magnetic field couplings.
In initial tests on an integer quantum Hall device at a 5-tesla magnetic field, conductance measurements across bulk filling factors from 1 to 4 yielded tunnelling charges within 5 percent of a single electron charge. Diagonal conductance scans as a function of top-gate voltage and direct-current bias displayed characteristic Coulomb diamond patterns.
Fractional charge measurements
Measurements on a second device at a 13.5-tesla magnetic field resolved quasiparticle charges at several fractional filling factors. Quasiparticles tunnelling at filling factors 4/3, 5/3, 7/3, and a smaller resonance at 8/3 registered charges near one-third of an electron charge.
In contrast, filling factor 2/3 and a larger resonance at 8/3 produced charges near two-thirds of an electron charge, while filling factor 3/5 yielded a charge close to three-fifths of an electron charge. The study's theoretical calculations attribute the charge differences across hole-conjugate states to edge re-equilibration variations caused by the parity of downstream integer edge modes.
