Birefringent break up of Dirac fermions in a square optical lattice

TL;DR

This paper proposes a method to create and tune birefringent Dirac fermions in a square optical lattice with artificial magnetic fields, revealing new gapless excitations with tunable velocities.

Contribution

It introduces a novel lattice model with tunable artificial magnetic fields that produce birefringent Dirac fermions, expanding control over low-energy excitations in cold atom systems.

Findings

Birefringent Dirac cones with different 'speeds of light' can be realized.

Tuning parameters allows for a single Dirac cone and flat band formation.

Various perturbations affect the low-energy spectrum and topological defects.

Abstract

We generalize a proposal by Sorensen et al. [Phys. Rev. Lett. 94, 086803 (2005)] for creating an artificial magnetic field in a cold atom system on a square optical lattice. This leads us to an effective lattice model with tunable spatially periodic modulation of the artificial magnetic field and the hopping amplitude. When there is an average flux of half a flux quantum per plaquette the spectrum of low-energy excitations can be described by massless Dirac fermions in which the usually doubly degenerate Dirac cones split into cones with different "speeds of light" which can be tuned to give a single Dirac cone and a flat band. These gapless birefringent Dirac fermions arise because of broken chiral symmetry in the kinetic energy term of the effective low energy Hamiltonian. We characterize the effects of various perturbations to the low-energy spectrum, including staggered potentials, interactions, and domain wall topological defects.