Electron transitions for Dirac Hamiltonians with flat-bands under electromagnetic radiation and its application to the $\alpha-\mathcal{T}_3$ graphene model

In a system with a Dirac-like linear dispersion there are always states that fulfill the resonance condition for electromagnetic radiation of arbitrary frequency $\Omega$. When a flat band is present two kinds of resonant transitions are found. Considering the $\alpha-\mathcal{T}_3$ graphene model as a minimal model with a flat band and Dirac cones, and describing the dynamics using the interaction picture, we study the band transitions induced by an external electromagnetic field. We found that transitions depend upon the relative angle between the electron momentum and the electromagnetic field wave vector. For parallel incidence, the transitions are found using Floquet theory while for other angles perturbation theory is used. In all cases, the transition probabilities and the frequencies are found. For some special values of the parameter $\alpha$ or by charge doping, the system behaves as a three level or a two-level Rabi system. All these previous results were compared with numerical simulations. A good agreement was found between both. The obtained results are useful to provide a quantum control of the system.
Comment: 8 pages, 5 figures