Coherent bunching of anyons and dissociation in an interference experiment

Aharonov–Bohm interference of fractional quasiparticles in the quantum Hall effect generally reveals their elementary charge (e*)1–15. Recently, our interferometry experiments with several ‘particle states’ reported flux periods of ΔΦ = (e/e*)Φ0 (with Φ0 the flux quantum) at moderate temperatures16. Here we report interference measurements of ‘particle–hole conjugated’ states at filling factors ν = 2/3, 3/5 and 4/7, which revealed unexpected flux periodicities of ΔΦ = ν−1Φ0. The measured shot-noise Fano factor (F) of the partitioned quasiparticles in each of the quantum point contacts of the interferometer was F = ν (ref. 17) rather than that of the elementary charge F = e*/e (refs. 18,19). These observations indicate that the interference of bunched (clustered) elementary quasiparticles occurred for coherent pairs, triples and quadruplets, respectively. A small metallic gate (top gate), deposited in the centre of the interferometer bulk, formed an antidot (or a dot) when charged, thus introducing local quasiparticles at the perimeter of the (anti)dot. Surprisingly, such charging led to a dissociation of the ‘bunched quasiparticles’ and, thus, recovered the conventional flux periodicity set by the elementary charge of the quasiparticles. However, the shot-noise Fano factor (of each quantum point contact) consistently remained at F = ν, possibly due to the neutral modes accompanying the conjugated states. The two observations—bunching and debunching (or dissociation)—were not expected by current theories. Similar effects may arise in Jain’s ‘particle states’ (at lower temperatures) and at even denominator fractional quantum Hall states20.