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, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14-15. Recently, our interferometry experiments with several 'particle states' reported flux periods of Delta Phi = (e/e*)Phi 0 (with Phi 0 the flux quantum) at moderate temperatures16. Here we report interference measurements of 'particle-hole conjugated' states at filling factors nu = 2/3, 3/5 and 4/7, which revealed unexpected flux periodicities of Delta Phi = nu-1 Phi 0. The measured shot-noise Fano factor (F) of the partitioned quasiparticles in each of the quantum point contacts of the interferometer was F = nu (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 = nu, 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.