Phase transitions and bunching of correlated particles in a non-Hermitian quasicrystal

TL;DR

This paper explores how two interacting particles behave in a non-Hermitian quasi crystal, revealing unique phenomena like lower transition thresholds for doublons and non-Hermitian particle bunching.

Contribution

It uncovers the effects of interactions on spectral transitions and introduces the novel concept of non-Hermitian particle bunching in a quasi crystal.

Findings

Doublon states have lower thresholds for localization-delocalization transitions.

Long-lived doublons tend to bunch together over time.

Spectral and dynamical features are influenced by non-Hermitian topology.

Abstract

Non-interacting particles in non-Hermitian quasi crystals display localization-delocalization and spectral phase transitions in complex energy plane, that can be characterized by point-gap topology. Here we investigate the spectral and dynamical features of two interacting particles in a non-Hermitian quasi crystal, described by an effective Hubbard model in an incommensurate sinusoidal potential with a complex phase, and unravel some intriguing effects without any Hermitian counterpart. Owing to the effective decrease of correlated hopping introduced by particle interaction, doublon states, i.e. bound particle states, display a much lower threshold for spectral and localization-delocalization transitions than single-particle states, leading to the emergence of mobility edges. Remarkably, since doublons display longer lifetimes, two particles initially placed in distant sites tend to bunch and stick together, forming a doublon state in the long time limit of evolution, a phenomenon that can be dubbed {\em non-Hermitian particle bunching}.