Continuous Transition between Bosonic Fractional Chern Insulator and Superfluid

TL;DR

This paper demonstrates a direct numerical observation of a continuous phase transition from a bosonic fractional Chern insulator to a superfluid, confirming theoretical predictions and exploring critical behavior in topological quantum phases.

Contribution

It provides the first direct numerical evidence of a continuous FCI-SF transition in bosonic systems, analyzing critical exponents and entanglement properties.

Findings

The FCI-SF(Γ) transition is continuous, while FCI-SF(M) is first-order.

Critical exponents are consistent with the 3D XY universality class.

The transition can be realized by tuning the band dispersion in ultracold atom systems.

Abstract

The properties of fractional Chern insulator (FCI) phases and the phase transitions between FCI and Mott insulators (MI) in bosonic systems are well studied. The continuous transitions between FCI and superfluid (SF), however, despite the inspiring field theoretical predictions, have not been directly verified. The existing numerical results of the FCI-SF transition are either indirect or clearly first-order. Here, by simply tuning the bandwidth of the Haldane honeycomb lattice model, we find direct transitions from a bosonic FCI at $\nu=1/2$ filling of a flat Chern band to two SF states with bosons condensed at momenta M or $\Gamma$, respectively. While the FCI-SF(M) transition is first-order, the FCI-SF($\Gamma$) transition is found continuous, and the bipartite entanglement entropy at the critical point with the area-law scaling is consistent with the critical theories. Through finite size criticality analysis, the obtained critical exponents $\beta\approx$ 0.35(5) and $\nu\approx$ 0.62(12) are both compatible with those of the 3D XY universality class within numerical uncertainty and possibly more exotic beyond-Landau ones. This letter thence presents a direct numerical demonstration of a continuous FCI-SF transition between topologically ordered phase and spontaneous continuous symmetry-breaking phase, and further indicates the zero-field bosonic FCI might be realized from a SF state by gradually flattening the dispersion of the Chern band, through the (quasi)adiabatic preparation in ultracold atom systems.