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.