Activation gaps are determined for fractional quantum Hall states with up to seven filled Landau levels of composite fermions carrying two vortices, which correspond to electron filling factors of up to 7/15 along the sequence $\nu =n/(2n+1).$ Systems with as many as 100 composite fermions are studied for this purpose. The relevance of the results to the issues of composite-fermion mass and the stability of fractional quantum Hall effect along the sequence $n/(2n+1)\mathrm{}$ is discussed.

• Received 27 March 2002

DOI:https://doi.org/10.1103/PhysRevB.66.155320