Gapless layered three-dimensional fractional quantum Hall states

Using the parton construction, we build a three-dimensional (3D) multilayer fractional quantum Hall state with average filling ν=1/3 per layer that is qualitatively distinct from a stacking of weakly coupled Laughlin states. The state supports gapped charge e/3 fermionic quasiparticles that can propagate both within and between the layers, in contrast to the quasiparticles in a multilayer Laughlin state which are confined within each layer. Moreover, the state has gapless neutral collective modes, a manifestation of an emergent "photon," which is minimally coupled to the fermionic quasiparticles. The surface sheath of the multilayer state resembles a chiral analog of the Halperin-Lee-Read state, which is protected against gap-forming instabilities by the topological character of the bulk 3D phase. We propose that this state might be present in multilayer systems in the "intermediate tunneling regime," where the interlayer tunneling strength is on the same order as the Coulomb energy scale. We also find that the parton construction leads to a candidate state for a bilayer ν=1/3 system in the intermediate tunneling regime. The candidate state is distinct from both a bilayer of ν=1/3 Laughlin states and the single layer ν=2/3 state but is, nonetheless, a fully gapped fractional quantum Hall state with charge e/3 anyonic quasiparticles.