Fractional Quantum Hall Effect of Composite Fermions

In a GaAs/AlGaAs quantum well of density 1×10¹¹ cm^-2 we observed a fractional quantum Hall effect (FQHE) at ν=4/11 and 5/13, and weaker states at ν=6/17, 4/13, 5/17, and 7/11. These sequences of fractions do not fit into the standard series of integral quantum Hall effects of composite fermions (CF) at ν=p/(2mp±1). They rather can be regarded as the FQHE of CFs attesting to residual interactions between these composite particles. In tilted magnetic fields the ν=4/11 state remains unchanged, strongly suggesting it to be spin polarized. The weak ν=7/11 state vanishes quickly with tilt.