Ultracold fermions in a one-dimensional bipartite optical lattice: metal-insulator transitions driven by shaking

TL;DR

This paper investigates how periodic shaking of a bipartite optical lattice can induce metal-insulator transitions in ultracold fermions, revealing novel metallic phases with four Fermi points influenced by interactions.

Contribution

It introduces a Floquet-based effective model for driven fermionic systems and explores the emergence of a four Fermi-point metallic phase under interactions, contrasting with traditional Hubbard models.

Findings

Periodic driving suppresses insulating behavior at half-filling.

A four Fermi-point metallic phase can be realized with specific driving parameters.

Interactions modify the stability and extent of the unconventional metallic phase.

Abstract

We describe the behavior of a system of fermionic atoms loaded in a bipartite one-dimensional optical lattice that is under the action of an external time-periodic driving force. By using Floquet theory, an effective model with renormalized hopping coefficients is derived. The insulating behavior characterizing the system at half-filling in the absence of driving is dynamically suppressed and for particular values of the driving parameter the system becomes either a standard metal or an unconventional metal with four Fermi points. We use the bosonization technique to investigate the effect of on-site Hubbard interactions on the four Fermi-point metal-insulator phase transition. Attractive interactions are expected to enlarge the regime of parameters where the unconventional metallic phase arises, whereas repulsive interactions reduce it. This metallic phase is known to be a Luther-Emery liquid (spin gapped metal) for both, repulsive and attractive interactions, contrarily to the usual Hubbard model which exhibits a Mott insulator phase for repulsive interactions. Ultracold fermions in driven one-dimensional bipartite optical lattices provide an interesting platform for the realization of this long studied four Fermi-point unconventional metal.