Laughlin topology on fractal lattices without area law entanglement

Laughlin states have recently been constructed on fractal lattices, and the charge and braiding statistics of the quasiholes were used to confirm that these states have Laughlin-type topology. Here we investigate density, correlation, and entanglement properties of the states on a fractal lattice derived from a Sierpinski triangle with the purpose of identifying similarities and differences compared to two-dimensional systems and with the purpose of investigating whether various probes of topology work for fractal lattices. Similarly to two-dimensional systems, we find that the connected particle-particle correlation function decays roughly exponentially with the distance between the lattice sites measured in the two-dimensional plane, but the values also depend on the local environment. Contrary to two-dimensional systems, we find that the entanglement entropy does not follow the area law if one defines the area to be the number of nearest-neighbor bonds that cross the edge of the selected subsystem. Considering bipartitions with two bonds crossing the edge, we find a close to logarithmic scaling of the entanglement entropy with the number of sites in the subsystem. This also means that the topological entanglement entropy cannot be extracted using the Kitaev-Preskill or the Levin-Wen methods. Studying the entanglement spectrum for different bipartitions, we find that the number of states below the entanglement gap is robust and the same as for Laughlin states on two-dimensional lattices.

Automated summary

This article investigates the density, correlation, and entanglement properties of Laughlin states on fractal lattices compared to two-dimensional systems. It is found that the connected particle-particle correlation function follows an exponential decay. However, unlike two-dimensional systems, the entanglement entropy does not follow the area law on fractal lattices. Additionally, the topological entanglement entropy cannot be extracted using the Kitaev-Preskill or the Levin-Wen methods. The entanglement spectrum for different partitions is also studied, and the number of states below the entanglement gap is found to be robust and the same as for Laughlin states on two-dimensional lattices.