Fractional quantum Hall effect of composite fermions

In a GaAs/AlGaAs quantum well of density 1x10(11) cm(-2) we observed a fractional quantum Hall effect (FQHE) at nu=4/11 and 5/13, and weaker states at nu=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 nu=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 nu=4/11 state remains unchanged, strongly suggesting it to be spin polarized. The weak nu=7/11 state vanishes quickly with tilt.