Analytical study of hybrid surface plasmon polaritons in a grounded chiral slab waveguide covered with graphene sheet

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Analytical study of hybrid surface plasmon polaritons in a grounded chiral slab waveguide covered with graphene sheet Mohammad Bagher Heydari1 · Mohammad Hashem Vadjed Samiei1  Received: 22 April 2020 / Accepted: 29 August 2020 © Springer Science+Business Media, LLC, part of Springer Nature 2020

Abstract In this paper, we propose a new analytical model for grounded chiral slab waveguides covered with graphene sheets. The general waveguide is constructed of a graphene sheet sandwiched between two different chiral layers (as substrate and cover layers), each one has the permittivity, the permeability and the chirality of 𝜀c , 𝜇c , 𝛾c , respectively. The substrate is supposed to be a perfect electromagnetic conductor, which is able to easily convert to a perfect electric conductor or a perfect magnetic conductor. A novel matrix representation is obtained for the general structure to find its dispersion relation and other propagating parameters. To show the richness of the proposed waveguide, two new structures have been introduced and investigated. It has been shown that the modal properties of these exemplary structures are tunable by changing the chemical potential of the graphene and the chirality. The proposed general structure and its analytical model can be utilized for designing tunable plasmonic devices in THz frequencies. Keywords  Analytical model · Graphene sheet · Chiral medium · Plasmson · PEMC · Effective index

1 Introduction Nowadays, graphene plasmonics is a new emerging science, which studies the excitation of surface plasmon polaritons (SPPs) on the graphene (Gonçalves and Peres 2016; Garcia de Abajo 2014; Huang et al. 2016). Due to some fascinating features of these SPPs, such as high mode confinement, a large variety of graphene-based devices have been reported at THz frequencies, such as waveguides (Heydari and Samiei 2018; Heydari and Vadjed Samiei 2020; Heydari and Samiei 2020a, b; Čtyroký et al. 2020; Parvaei et al. 2018; Pitilakis et al. 2016), and absorbers (Dave et al. 2018; Arsanjani et al. 2019; Patel et al. 2019). Chiral materials, one of the interesting materials in chemistry science with many remarkable features such as optical activity and circular dichroism, have opened a new area for

* Mohammad Hashem Vadjed Samiei [email protected] 1



School of Electrical Engineering, Iran University of Science and Technology (IUST), Tehran, Iran

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M. B. Heydari, M. H. Vadjed Samiei

researchers to design and report innovative devices such as cloak (Zeng and Song 2017), polarization rotator (Ye and He 2010) and microstrip antenna (Pozar 1992). The hybridization of graphene and chiral medium in a THz device is very fascinating because the plasmonic features of the proposed device can be controlled and adjusted simultaneously by changing the chirality and the chemical potential of the graphene (Yaqoob et al. 2018, 2019; Toqeer et al. 2019). For instance, the modal properties of a graphene-chiral interface have been discussed and studied in (Yaqoob e