Neven Golenić and Vito Despoja, together with a collaborator from Italy Stefano de Gironcoli, published a paper in npj 2D Materials and Applications, where they theoretically examined the Bloch plasmon polaritons band structure in Al₂O₃/graphene/hexagonal-boron-nitride/graphene nanoribbons assembly  depending on the doping of graphene systems.

Tailored plasmon polariton landscape in graphene/boron nitride patterned heterostructures

Neven Golenić, Stefano de Gironcoli and Vito Despoja, npj 2D Mater Appl 8, 37 (2024)

DOI: 10.1038/s41699-024-00469-6

Surface plasmon polaritons (SPPs), which are electromagnetic modes representing collective oscillations of charge density coupled with photons, have been extensively studied in graphene. This has provided a solid foundation for understanding SPPs in 2D materials. However, the emergence of wafer-transfer techniques has led to the creation of various quasi-2D van der Waals heterostructures, highlighting certain gaps in our understanding of their optical properties in relation to SPPs. To address this, we analyzed electromagnetic modes in graphene/hexagonal-boron-nitride/graphene-nanoribbons heterostructures on a dielectric Al₂O₃ substrate using the full ab initio RPA optical conductivity tensor. We demonstrate that patterning of the topmost graphene into nanoribbons provides efficient Umklapp scattering of the graphene Dirac plasmon polariton (DP) into the radiative region, resulting in the conversion of the DP into a robust infrared-active plasmon. Additionally, we show that the optical activity of the DP and its hybridization with inherent plasmon resonances in graphene nanoribbons are highly sensitive to the doping of both the topmost and bottommost graphene layers (Fig.1). By elucidating these optical characteristics, we aspire to catalyze further advancements and create new opportunities for innovative applications in photonics and optoelectronic integration.

Figure 1. Bloch-Dirac plasmon band structure arising in GNR/h-BN/GR/Al₂O₃ assembly. Intensities of electromagnetic modes as a function of top (n_GNR) and bottom (n_GR) layer charge carrier doping. (a) n_GNR=0 e cm⁻² ,n_GR=1×10¹⁴ e cm⁻² ; (b) n_GNR=1×10¹³ e cm⁻², n _GR=1×10¹⁴ e cm⁻²; (c)n_GNR=2×10¹³ e cm⁻², n_GR=1×10¹⁴ e cm⁻²; (d)n _GNR=1×10¹⁴ e cm⁻² ,n ^GR=0 e cm⁻²; (e)n_GNR=1×10¹⁴ e cm⁻², n_GR=1×10¹³ e cm⁻²; (f)n _GNR=1×10¹⁴ e cm⁻², n_GR = 1×10 ¹⁴ e cm⁻² . The Dirac plasmons DP1/DP2′ and DP1’/DP2 in the bottom GR layer (yellow) scatter on topmost GNR forming Bloch plasmon polariton modes BP1 and BP1* (red). The GNR by itself supports plasmon resonances PR0, PR1, PR2,… (blue) which hybridise with DP1/DP2′ and DP1’/DP2 to form lower (L-DP) and upper (U-DP) polaritonic branches (yellow+blue).