Numerical study of fractional quantum Hall electron-hole systems: Evidence of stable anyonic ions

Spatially separated electron-hole layers in strong magnetic fields are studied by exactly diagonalizing the Hamiltonian of a small number of particles. When the separation between layers is of the same order as the intralayer particle separation, the ground-state energy of the system displays a pronounced cusp as a function of the Landau level degeneracy at an odd denominator fraction {ν}̃ \~c, where {ν}̃ \~c==(νₑ-νₕ)/(1-νₕ), and νₑ and νₕ are the electron and hole filling factors (νₕ{}νₑ). Detailed analysis suggests that the ground state responsible for the cusp consists of stable ions (composed of Laughlin quasiparticles bound to a hole) weakly coupled to an incompressible fluid state of the remaining electrons.