Band spectra of periodic hybrid $δ$-$δ^\prime$ structures
We present a detailed study of a generalised one-dimensional Kronig-Penney model using $δ\text{-}δ'$ potentials. We analyse the band structure and the density of states in two situations. In the first case we consider an infinite array formed by identical $δ\text{-}δ'$ potentials standing at the linear lattice nodes. This case will be known throughout the paper as the one-species hybrid Dirac comb. We investigate the consequences of adding the $δ'$ interaction to the Dirac comb by comparing the band spectra and the density of states of pure Dirac-$δ$ combs and one-species hybrid Dirac combs. Secondly we study the quantum system that arises when the periodic potential is the one obtained from the superposition of two one-species hybrid Dirac combs displaced one with respect to the other and with different couplings. The latter will be known as the two-species hybrid Dirac comb. One of the most remarkable results is the appearance of a curvature change in the band spectrum when the $δ'$ couplings are above a critical value.