ORIGIN OF THE UPSILON=2/5 FRACTIONAL QUANTUM HALL-EFFECT

We present numerical evidence in support of the view that the physical origin of the fractional quantum Hall effect at v = n/(2n + 1) is associated with the fact that this is the largest filling factor at which an n-component system of electrons can avoid having any pair of electrons occur in a state of relative angular momentum 1. Our calculations, for n = 2, are based on a model in which the Hilbert space is truncated to the two lowest Landau levels and the Landau-level separation, HBAR-omega-c, is a parameter of the model. For HBAR-omega-c = 0 and short-range repulsive interactions, a zero-energy incompressible ground state occurs at v = 2/5. Our numerical results suggest that, in agreement with arguments advanced by J. K. Jain, this incompressibility survives to the strong-field limit HBAR-omega-c = infinity.