Floquet Engineering of Haldane Chern Insulators and Chiral bosonic phase transitions

TL;DR

This paper uses Floquet engineering to create topologically non-trivial Haldane models and induce quantum phase transitions in bosonic systems, revealing new phases and edge states in driven lattice systems.

Contribution

It demonstrates how Floquet theory can engineer anisotropic Haldane models with topological properties and induce a superfluid to BEC-FFLO phase transition in bosonic lattices.

Findings

Topologically non-trivial band structures with chiral edge modes

Quantum phase transition between superfluid and BEC-FFLO states

Validation of high-frequency Floquet expansion through simulations

Abstract

The realization of synthetic gauge fields has attracted a lot of attention recently in relation with periodically driven systems and the Floquet theory. In ultra-cold atom systems in optical lattices and photonic networks, this allows to simulate exotic phases of matter such as quantum Hall phases, anomalous quantum Hall phases and analogs of topological insulators. In this paper, we apply the Floquet theory to engineer anisotropic Haldane models on the honeycomb lattice and two-leg ladder systems. We show that these anisotropic Haldane models still possess a topologically non-trivial band structure associated with chiral edge modes (without the presence of a net unit flux in a unit cell), then referring to the quantum anomalous Hall effect. Focusing on (interacting) boson systems in s-wave bands of the lattice, we show how to engineer through the Floquet theory, a quantum phase transition between a uniform superfluid and a BEC (Bose-Einstein Condensate) analog of FFLO (Fulde-Ferrell-Larkin-Ovchinnikov) states, where bosons condense at non-zero wave-vectors. We perform a Ginzburg-Landau analysis of the quantum phase transition on the graphene lattice, and compute observables such as chiral currents and the momentum distribution. The results are supported by exact diagonalization calculations and compared with those of the isotropic situation. The validity of high-frequency expansion in the Floquet theory is also tested using time-dependent simulations for various parameters of the model. Last, we show that the anisotropic choice for the effective vector potential allows a bosonization approach in equivalent ladder (strip) geometries.