Plasmonic 2D Quasicrystals with Different Orientational Order for Strong Light-Matter Interaction

Numerous systems, from biological structures to solid-state devices, are driven by light-matter interaction. In many cases, this interaction is rather weak and such that the electromagnetic radiation can be treated as an external perturbation to materials. However, under specific circumstances, the energy exchange rate between light and matter can become faster than any other relaxation process and the system can enter the strong coupling regime. Hybrid light-matter states, called polaritons, emerge with an energy separation, known as Rabi splitting, dependent on the coupling strength. Strong light-matter interaction can thus be used as a tool to fundamentally reshape the material properties, with significant implications on technologically-relevant processes in various fields, spanning from photocatalysis to optoelectronic and quantum technologies [1].<br/>Within the polariton panorama, particular interest has been addressed towards polaritonic systems in which quantum emitters, such as dye molecules and low-dimensional semiconductors, are integrated with plasmonic architectures. Among the proposed plasmonic platforms, 2D periodic nanohole arrays supporting surface plasmon polariton Bloch waves (SPP-BWs), <i>i.e.</i> standing waves of propagating SPPs, were extensively used since they are characterized by a planar and open architecture which facilitates both the placement of the excitonic material and, in the hybrid system, the excitation and probing of polaritons. Moreover, their main resonance features can be finely tuned by acting on both the array symmetry (<i>i.e.</i> hole arrangement) and geometry (<i>i.e. </i>inter-hole distance and hole diameter) [2]. Additional degrees of freedom in the design of the plasmonic component can be offered by the exploitation of metasurfaces lacking periodic translational order. Quasicrystals (QCs), ordered structures with a long-range quasiperiodic translational order and a long-range orientational order, belong to this category. In the reciprocal space, they are indeed characterized by a high density of diffraction peaks, which provides a quasi-isotropic multi-k-vector system with highly tunable optical properties [3].<br/>Here, we show that QCs can be used as a platform extension beyond crystal-like nanohole metasurfaces to be integrated with quantum emitters for the realization of strongly-coupled hybrid devices. Nanohole patterns characterized by diverse quasicrystalline configurations were milled through an optically-thick silver film and coupled to J-aggregates of TDBC dye. Steady-state transmittance spectroscopy was employed to investigate the radiative properties of the hybrid structure. The presence of the anti-crossing behavior, as one of the distinctive fingerprint of strong-coupling regime, was assed and investigated. Moreover, our results highlight that the exploitation of quasiperiodic arrays generated by different tilings allows to obtain plasmonic structures with distinctive symmetry-dependent resonance features and, thus, enables the realization of polaritonic systems with tailored properties. More in general, our findings may inspire further exploration towards novel heterostructures, where plasmonic 2D quasicrystals are combined with low-dimensional semiconductors, such as quantum dots or 2D materials.<br/><br/>This work is part of the REPLY project that received funding from the European Research Council (ERC) under the European Union’s Horizon 2020 research and innovation program (grant agreement No 101002422).<br/><br/>[1] F. J. Garcia-Vidal, <i>et al. </i>Science 373, eabd0336 (2021)<br/>[2] H. Wang, <i>et al. </i>Adv. Funct. Mater. 28, 1801761 (2018)<br/>[3] D. Levine, <i>et al.</i>Phys. Rev. B 34, 596 (1986)