Magneto-optical evidence for fractional quantum Hall states down to filling factor 1/9

Discontinuities have been observed in the energy dependence on magnetic field of the luminescence line corresponding to 2D electron-hole recombination in GaAs/AlGaAs heterojunctions at filling factors {ν}=2/3, 1/3, 4/5, 3/5, 2/5, 1/5, 1/7, and 1/9. We associate these energy-position shifts with discontinuous behavior of the chemical potential due to condensation of the 2D electrons into an incompressible Fermi-liquid state, and thereby evaluate the energy gaps at fractional filling factors down to 1/9.