Excitons in the fractional quantum Hall effect

Abstract

Excitons, Coulomb-driven bound states of electrons and holes, are typically composed of integer charges^1,2. However, in bilayer systems influenced by charge fractionalization^3,4, a more interesting form of interlayer exciton can emerge, in which pairing occurs between constituents that carry fractional charges. Despite numerous theoretical predictions for these fractional excitons^{5,6,7,8,9,10,11,12,13,14,15,16}, their experimental observation has remained unexplored. Here we report transport signatures of excitonic pairing in fractional quantum Hall effect states. By probing the composition of these excitons and their impact on the underlying wavefunction, we discover two new types of quantum phases of matter. One of these can be viewed as the fractional counterpart of the exciton condensate at a total filling of 1, whereas the other involves a more unusual type of exciton that obeys non-bosonic quantum statistics, challenging the standard model of bosonic excitons.