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Abstract <p>The research proves bilayer plasmonic metasurfaces with engineered twist angles giving rise to Moiré superlattices sustaining topologically nontrivial edge states in broken time-reversal symmetry (TRS). The structures were realized by high-resolution electron-beam lithography with rotational misalignment accuracy of 0.1° precision. Structural homogeneity was confirmed by SEM and AFM with spacer thickness of 30 ± 2&#xa0;nm and interlayer misfit less than 3&#xa0;nm. Fourier-transform infrared spectroscopy (FTIR) detected twist-angle-dependent plasmonic bandgaps, with the maximum bandgap (~ 50&#xa0;nm) at θ = 5°. Unidirectional edge states were verified with and without magnetic bias or in YIG substrates by near-field scanning optical microscopy (NSOM). Finite-difference time-domain (FDTD) and COMSOL simulations simulated experimental positions of bandgaps and wavelengths of edge modes with ~ 10&#xa0;nm accuracy. Simulations also showed good field confinement and maximum Q-factor of ~ 250 at θ = 5°. Results indicate that by incorporating twist-angle engineering along with time-reversal symmetry (TRS)—breaking mechanisms, one has a versatile platform for reconfigurable photonic topological devices for nanoscale routing, sensing, and optical isolation.</p> Graphical abstract <p>The concept in Fig.&#xa0;<InternalRef RefID="Fig1">1</InternalRef> of this research is to shape bilayer plasmonic metasurfaces with set twist angles, which leads to Moiré superlattices able to produce plasmonic bandgaps and topologically protected edge states. Shifting the position of one nanostructure layer relative to another changes the interaction between the layers, which creates both new periodicities and new types of plasmons. With the help of yttrium iron garnet (YIG) or external magnetic fields that break time-reversal symmetry (TRS), the system permits plasmons to move in only one direction along its edges. This makes it possible to design optical states that work well and are easy to control for use in topological photonic devices.</p>

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Topological edge states in twist-engineered Moiré plasmonic metasurfaces under magnetic time-reversal symmetry breaking

  • 期刊论文

  • 发表日期：

    2025年12月13日

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  • Rishab chaturvedi,
  • N. Nagabhooshanam,
  • Prahalad Singh Parihar,
  • Nilesh Bhosle,
  • S. Supriya,
  • V. S. N. Kumar,
  • A. Rajaram

摘要

Abstract

The research proves bilayer plasmonic metasurfaces with engineered twist angles giving rise to Moiré superlattices sustaining topologically nontrivial edge states in broken time-reversal symmetry (TRS). The structures were realized by high-resolution electron-beam lithography with rotational misalignment accuracy of 0.1° precision. Structural homogeneity was confirmed by SEM and AFM with spacer thickness of 30 ± 2 nm and interlayer misfit less than 3 nm. Fourier-transform infrared spectroscopy (FTIR) detected twist-angle-dependent plasmonic bandgaps, with the maximum bandgap (~ 50 nm) at θ = 5°. Unidirectional edge states were verified with and without magnetic bias or in YIG substrates by near-field scanning optical microscopy (NSOM). Finite-difference time-domain (FDTD) and COMSOL simulations simulated experimental positions of bandgaps and wavelengths of edge modes with ~ 10 nm accuracy. Simulations also showed good field confinement and maximum Q-factor of ~ 250 at θ = 5°. Results indicate that by incorporating twist-angle engineering along with time-reversal symmetry (TRS)—breaking mechanisms, one has a versatile platform for reconfigurable photonic topological devices for nanoscale routing, sensing, and optical isolation.

Graphical abstract

The concept in Fig. 1 of this research is to shape bilayer plasmonic metasurfaces with set twist angles, which leads to Moiré superlattices able to produce plasmonic bandgaps and topologically protected edge states. Shifting the position of one nanostructure layer relative to another changes the interaction between the layers, which creates both new periodicities and new types of plasmons. With the help of yttrium iron garnet (YIG) or external magnetic fields that break time-reversal symmetry (TRS), the system permits plasmons to move in only one direction along its edges. This makes it possible to design optical states that work well and are easy to control for use in topological photonic devices.