Equivalence and superposition of real and imaginary quasiperiodicities

TL;DR

This paper demonstrates the equivalence and superposition effects of real and imaginary quasiperiodic potentials in inducing localization in non-Hermitian models, revealing their coherence, universality, and phase behavior through analytical and numerical analysis.

Contribution

It analytically proves the equivalence of real and imaginary quasiperiodic potentials and explores their superposition effects on localization, linking models to the same universality class.

Findings

Real and imaginary QPs induce localization equivalently.

Superposed QPs with same frequency are coherent in localization.

Incoherent superpositions lead to earlier localization and mixed phases.

Abstract

We take non-Hermitian Aubry-Andr\'{e}-Harper models and quasiperiodic Kitaev chains as examples to demonstrate the equivalence and superposition of real and imaginary quasiperiodic potentials (QPs) on inducing localization of single-particle states. We prove this equivalence by analytically computing Lyapunov exponents (or inverse of localization lengths) for systems with purely real and purely imaginary QPs. Moreover, when superposed and with the same frequency, real and imaginary QPs are coherent on inducing the localization, under a way which is determined by the relative phase between them. The localization induced by a coherent superposition can be simulated by the Hermitian model with an effective strength of QP, implying that models are in the same universality class. When their frequencies are different and relatively incommensurate, they are incoherent and their superposition leads to less correlation effects. Numerical results show that the localization happens earlier and there is an intermediate mixed phase lacking of mobility edge.