Exact mobility line and mobility ring in the complex energy plane of a flat-band lattice with a non-Hermitian quasiperiodic potential
Phys. Rev. B 111, 214205 – Published 10 June, 2025
DOI: https://doi.org/10.1103/z96m-ckm6
Abstract
In this study, we investigate the problem of Anderson localization in a one-dimensional flat band lattice with a non-Hermitian quasiperiodic on-site potential. First of all, we discuss the influences of non-Hermitian potentials on the existence of critical states. Our findings show that, unlike in Hermitian cases, the non-Hermiticity of the potential leads to the disappearance of critical states and critical regions. Furthermore, we are able to accurately determine the Lyapunov exponents and the mobility edges. Our results reveal that the mobility edges form mobility lines and mobility rings in the complex energy plane. Within the mobility rings, the eigenstates are extended, while the localized states are located outside the mobility rings. For mobility line cases, only when the eigenenergies lie on the mobility lines, their corresponding eigenstates are extended states. As the energy approaches the mobility edges, we observe that, differently from Hermitian cases, here the critical index of the localization length is not a constant, but rather varies depending on the positions of the mobility edges. In addition, we conducted a comprehensive study on the effects of different parameter changes on the phase diagram of the system. Finally, we find that the changes of parameters can lead to changes of the topological structure of the mobility rings.
