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The fractional quantum Hall (FQH) effect is a canonical example ofelectron-electron interactions producing new ground states in many-bodysystems. Most FQH studies have focused on the lowest Landau level (LL), whosefractional states are successfully explained by the composite fermion (CF)model, in which an even number of magnetic flux quanta are attached to anelectron and where states form the sequence of filling factors $\nu = p/(2mp\pm 1)$, with $m$ and $p$ positive integers. In the widely-studied GaAs-basedsystem, the CF picture is thought to become unstable for the $N \geq 2$ LL,where larger residual interactions between CFs are predicted and competingmany-body phases have been observed. Here we report transport measurements ofFQH states in the $N=2$ LL (filling factors $4 < \nu < 8$) in bilayer graphene,a system with spin and valley degrees of freedom in all LLs, and an additionalorbital degeneracy in the 8-fold degenerate $N=0$/$N=1$ LLs. In contrast withrecent observations of particle-hole asymmetry in the $N=0$/$N=1$ LLs ofbilayer graphene, the FQH states we observe in the $N=2$ LL are consistent withthe CF model: within a LL, they form a complete sequence of particle-holesymmetric states whose relative strength is dependent on their denominators.The FQH states in the $N=2$ LL display energy gaps of a few Kelvin, comparableto and in some cases larger than those of fractional states in the $N=0$/$N=1$LLs. The FQH states we observe form, to the best of our knowledge, the highestset of particle-hole symmetric pairs seen in any material system.

Robust fractional quantum Hall effect and composite fermions in the $N=2$ Landau level in bilayer graphene