Trifurcation of band-gap structure and coexistence of lattice-like states and critical states in piezoelectric period-doubling superlatticesZ. X. Liu, L. M. Wang, H. He and W. Y. ZhangEur. Phys. J. B, 59 2 (2007) 179-184DOI: https://doi.org/10.1140/epjb/e2007-00286-0