Continuous Transition between Bosonic Fractional Chern Insulator and Superfluid

Area of Science:

• Condensed Matter Physics
• Topological Phases of Matter
• Quantum Simulation

Background:

• Fractional Chern insulator (FCI) phases and their transitions to Mott insulators are well-understood.
• Continuous transitions between FCIs and superfluids (SFs) lack direct numerical verification, despite theoretical predictions.
• Existing numerical studies of FCI-SF transitions are indirect or indicate first-order transitions.

Purpose of the Study:

• To numerically demonstrate a continuous transition between bosonic fractional Chern insulator (FCI) phases and superfluid (SF) states.
• To investigate the nature of the FCI-SF transition by tuning the bandwidth in the Haldane honeycomb lattice model.
• To provide a direct experimental pathway for realizing topological phases in ultracold atom systems.

Main Methods:

• Utilized the Haldane honeycomb lattice model for bosonic systems.
• Tuned the bandwidth of the flat Chern band to induce phase transitions.
• Performed finite-size criticality analysis and calculated bipartite entanglement entropy.

Main Results:

• Observed direct transitions from a bosonic FCI at ν=1/2 filling to two SF states (condensed at M or Γ momenta).
• Identified a continuous FCI-SF(Γ) transition, distinct from the first-order FCI-SF(M) transition.
• Calculated critical exponents (β≈0.35(5), ν≈0.62(12)) consistent with the 3D XY universality class.

Conclusions:

• Presented the first direct numerical demonstration of a continuous transition between a topologically ordered FCI and a symmetry-breaking SF phase.
• The findings support the possibility of realizing bosonic FCIs from SF states via band flattening in ultracold atom experiments.
• The observed critical exponents suggest potential connections to both established and exotic universality classes.