Two-body interaction induced phase transitions and intermediate phases in nonreciprocal non-Hermitian quasicrystals

TL;DR

This paper explores how interactions and nonreciprocal hopping in non-Hermitian quasicrystals lead to novel phase transitions, including intermediate mobility edge phases and tunable non-Hermitian skin effects for bosonic pairs.

Contribution

It introduces a framework to analyze the combined effects of interactions and nonreciprocity on localization, topological phases, and skin effects in non-Hermitian quasiperiodic systems.

Findings

Interactions enlarge the localization transition point.

Localized doublons exhibit non-Hermitian skin effects.

Skin localization can be tuned by hopping parameters.

Abstract

Non-Hermitian phenomena, such as exceptional points, non-Hermitian skin effects, and topologically nontrivial phases have attracted continued attention. In this work, we reveal how interactions and nonreciprocal hopping could collectively influence the behavior of two interacting bosons on quasiperiodic lattices. Focusing on the Bose-Hubbard model with Aubry-Andr\'e-Harper quasiperiodic modulations and hopping asymmetry, we discover that interactions could enlarge the localization transition point of the noninteracting system into an intermediate mobility edge phase, in which localized doublons formed by bosonic pairs can coexist with delocalized states. Under the open boundary condition, the bosonic doublons could further show non-Hermitian skin effects, realizing doublon condensation at the edges, and their direction of skin-localization can be flexibly tuned by the hopping parameters. A framework is developed to characterize the spectral, localization, and topological transitions accompanying these phenomena. Our work advances the understanding of localization and topological phases in non-Hermitian systems, particularly in relation to multiparticle interactions.