▎ 摘 要
Recent experiment reveals the appearance of incompressible fractional quantum Ilan effect states in monolayer graphene at nu = +/- 1/2 and +/- 1/4,+/- 3/4 substituting the compressible Hall metal states at these fillings in the lowest Landau level in a narrow magnetic field window depending on the sample parameters. Simultaneously, none such behavior has been observed either for nu = +/- 3/2 or +/- 5/4, +/- 7/4. We propose an explanation of these observations in terms of homotopy of monolayer graphene in consistence with a general theory of correlated states in planar Hall systems.