Excitation Spectrum of the Fractional Quantum Hall Effect: Two Component Fermion System

Two component, or pseudospin 1/2, fermion system in the lowest Landau level is investigated. The ground state at ν= 2/5, where ν is the filling factor of the lowest Landau level, has quite different character from that of ν= 1/3: In the former the total pseudospin is zero, while in the latter pseudospin is fully polarized. The excitation spectrum from these qualitatively different ground states are investigated numerically at small but finite momentum. The quasiparticles for these ground states are also investigated, and existence of those with charge ± e /5 at ν= 2/5 is shown. The knowledge of the quasiparticle charge makes extrapolation of the numerical results to infinite momentum possible, and activation energies are obtained.