The Nonlinear Optical Response of the α-T3 Lattice in the Terahertz Regime

We study the electronic contribution to the nonlinear optical response of the alpha-T-3 model. This model is an interpolation between a graphene (alpha=0) and dice or T-3 (alpha=1) lattice (Fig. 1.). Using a second-quantised formalism we calculate the first and third order responses for a range of alpha and chemical potential values as well as considering a band gap in the first-order case. Conductivity quantisation is observed in the first order, whilst Higher-order Harmonic Generation (HHG) is observed in the third order response with the chemical potential (mu) determining which applied field frequencies both quantisation and HHG occur at. We observe a range of experimentally accessible critical fields between 10(2)-10(6) V/m with dynamics depending on alpha, mu and applied field frequency. Our results suggest an alpha-T-3 could be an ideal candidate material for use in tunable terahertz devices.