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.