Beyond paired quantum Hall states: Parafermions and incompressible states in the first excited Landau level

The Pfaffian quantum Hall states, which can be viewed as involving pairing either of spin-polarized electrons or of composite fermions, are generalize d by finding the exact ground states of certain Hamiltonians with k+l-body interactions, for all integers k greater than or equal to l. The remarkably simple wave functions of these states involve clusters of k particles, and are related to correlators of parafermion currents in two-dimensional conf ormal field theory. The k=2 case is the Pfaffian. For k greater than or equ al to 2, the quasiparticle excitations of these systems are expected to pos sess non-Abelian statistics, like those of the Pfaffian. For k=3, these gro und states have large overlaps with the ground states of the (two-body) Cou lomb-interaction Hamiltonian for electrons in the first excited Landau leve l at total filling factors v= 2 + 3/5,2 + 2/5. [S0163-1829(99)06911-8]