Optical probing of composite fermions in a two-dimensional electron gas

In a high magnetic field, electrons confined to two dimensions form highly correlated states driven entirely by electron\u2013electron interactions. Transport and cyclotron-resonance experiments on these fractional quantum Hall effect states, and the associated fractionally charged excitations, suggest the existence of composite fermions\u2014electrons with two flux quanta attached. Using optical spectroscopy, we show that the two flux quanta in a composite fermion interacting with an exciton (a bound state of an electron and a hole) lead to filling-factor-dependent features in the optical emission spectrum, which are symmetric around filling factor nu=1/2, and fractionally charged excitations lead to fractionally charged excitons. In the vicinity of the incompressible nu=1/3 state we observe a doublet structure in the emission line, corresponding to excitations of the incompressible fluid. At filling factors nu>1/3, corresponding to the transition to a compressible metallic state20, a new emission line appears, which we attribute to the fractionally charged quasi-exciton.NRC publication: Ye