Non-Hermitian quasicrystal in dimerized lattices

Non-Hermitian quasicrystals possess PT and metal-insulator transitions induced by gain and loss or nonreciprocal effects.In this work,we uncover the nature of localization transitions in a generalized Aubry-Andre-Harper model with´dimerized hopping amplitudes and complex onsite potential.By investigating the spectrum,adjacent gap ratios and inverse participation ratios,we find an extended phase,a localized phase and a mobility edge phase,which are originated from the interplay between hopping dimerizations and non-Hermitian onsite potential.The lower and upper bounds of the mobility edge are further characterized by a pair of topological winding numbers,which undergo quantized jumps at the boundaries between different phases.Our discoveries thus unveil the richness of topological and transport phenomena in dimerized non-Hermitian quasicrystals.