Topological n -root Su-Schrieffer-Heeger model in a non-Hermitian photonic ring system
Viedma, David (Universitat Autònoma de Barcelona. Departament de Física)
Marques, Anselmo M. (Universidade de Aveiro)
Dias, Ricardo G. (Universidade de Aveiro)
Ahufinger, Verònica (Universitat Autònoma de Barcelona. Departament de Física)

Date:	2024
Abstract:	Square-root topology is one of the newest additions to the ever expanding field of topological insulators (TIs). It characterizes systems that relate to their parent TI through the squaring of their Hamiltonians. Extensions to 2 n -root topology, where n is the number of squaring operations involved in retrieving the parent TI, were quick to follow. Here, we go one step further and develop the framework for designing general n -root TIs, with n any positive integer, using the Su-Schrieffer-Heeger (SSH) model as the parent TI from which the higher-root versions are constructed. The method relies on using loops of unidirectional couplings as building blocks, such that the resulting model is non-Hermitian and embedded with a generalized chiral symmetry. Edge states are observed at the n branches of the complex energy spectrum, appearing within what we designate as a ring gap, shown to be irreducible to the usual point or line gaps. We further detail on how such an n -root model can be realistically implemented in photonic ring systems. Near perfect unidirectional effective couplings between the main rings can be generated via mediating link rings with modulated gains and losses. These induce high imaginary gauge fields that strongly suppress couplings in one direction, while enhancing them in the other. We use these photonic lattices to validate and benchmark the analytical predictions. Our results introduce a new class of high-root topological models, as well as a route for their experimental realization.
Grants:	Agència de Gestió d'Ajuts Universitaris i de Recerca 2021/SGR-00138 Agencia Estatal de Investigación PID2020-118153GB-I00
Rights:	Aquest document està subjecte a una llicència d'ús Creative Commons. Es permet la reproducció total o parcial, la distribució, la comunicació pública de l'obra i la creació d'obres derivades, fins i tot amb finalitats comercials, sempre i quan es reconegui l'autoria de l'obra original.
Language:	Anglès
Document:	Article ; recerca ; Versió publicada
Subject:	Topological photonics ; Ring resonators ; High-root topology ; Non-Hermitian systems ; Edge states
Published in:	Nanophotonics, Vol. 13, Issue 1 (January 2024) , p. 51-61, ISSN 2192-8614

DOI: 10.1515/nanoph-2023-0590
PMID: 39633993

11 p, 1.7 MB

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