PT-symmetric optical superlattices

The spectral and localization properties of $\mathcal{PT}$-symmetric optical superlattices, either infinitely extended or truncated at one side, are theoretically investigated, and the criteria that ensure a real energy spectrum are derived. The analysis is applied to the case of superlattices describing a complex ($\mathcal{PT}$-symmetric) extension of the Harper Hamiltonian in the rational case.