= 1/4 in Wide Quantum Wells**

For zero width systems, the ground state at filling factor ¼ is described by the fully polarized composite fermion Fermi sea. However, fractional quantum Hall effect (FQHE) has been observed at ¼ in wide quantum well samples [1]. We consider several single-component candidate states, and conclude that the non-Abelian “22111-parton” state is the most likely candidate. Our calculated phase diagram as a function of the quantum well width and the density is in very good agreement with experiments. We suggest further experiments that can confirm the nature of the ¼ state and, in particular, distinguish it from other candidate states. We also consider a bilayer system at total filling ¼ as a function of the interlayer separation and predict that it does not support any incompressible FQHE state.
[1] D. Luhman et al., Phys. Rev. Lett. 101, 266804 (2008).