Rydberg polaritons in ReS2 crystals

Annalisa Coriolano^a^,^b, Laura Polimeno^a, Luisa De Marco^a, Dario Ballarini^a, Daniele Sanvitto^a, Milena De Giorgi^a

^aCNR NANOTEC – Institute of Nanotechnology, c/o Campus Ecotekne, University of Salento, Via Monteroni, Lecce, 73100 Italy

^bUniversità del Salento, Lecce, Via per Monteroni, Lecce, Italy

Materials for Sustainable Development Conference (MATSUS)
Proceedings of MATSUS23 & Sustainable Technology Forum València (STECH23) (MATSUS23)

#QMat - Materials for Quantum Technology

VALÈNCIA, Spain, 2023 March 6th - 10th

Organizers: José J. Baldoví, Dmitry Baranov and Jannika Lauth

Oral, Annalisa Coriolano, presentation 164
DOI: https://doi.org/10.29363/nanoge.matsus.2023.164
Publication date: 22nd December 2022

Transition metal dichalcogenides (TMDs), such as WSe₂ or MoS₂, are van der Waals materials with exceptional properties, such as chemical stability and mechanical flexibility[1], high binding energies[2], [3], high oscillator strengths and narrow photoluminescence linewidths[4]. However, by changing the crystal thickness (from bulk to monolayer), they show a transition from indirect to direct bandgap and so the monolayer is strictly required. On the other hand, Rhenium disulfide (ReS₂) is a group-VII TMDs, with attractive properties, such as exceptionally high refractive index, significant oscillator strength and optical birefringence[5]. This envolves the formation of two orthogonally polarized in–plane excitons[6] induced by ReS₂ crystallization in a distorted single-layer trigonal structure of triclinic symmetry. It is worth nothing that these exceptional optical properties persist from bulk to monolayer, making possible to exploit the high refractive index of this material and to tune the characteristics of the nanophotonic devices by changing crystal thickness. In this work, we observed that for crystals with a thickness higher than 50 nm, the excitonic transitions show a fine structure observed in previous works in literature [6]–[9], but whose nature is widely debated. With our work we clearly demonstrate that this fine structure is due to the longitudinal and transverse exciton, which becomes evident in ReS₂ crystals thanks to the unique combination of its exceptional high refractive index and large exciton oscillator strength that ReS₂ possesses.

By transferring ReS₂ flake on a Distributed Bragg Reflector (DBR), we also observed a polarization-dependence strong coupling between Fabry-Perot modes and both excitons in the fundamental and Rydberg excited states,resulting in the formation of middle polariton branches. These show a strong polariton-polariton interaction which results in a blueshift of the polariton mode when the polariton density inside the system increases, that clearly reflect an outstanding interest of ReS₂ as a solid-state counterpart of Rydberg atomic systems. This study offers a complete interpretation of ReS₂ optical features, making this material interesting for a plethora of photonic applications and a novel platform for the exploration of topological properties.

References:

[1] W. Choi, N. Choudhary, G. H. Han, J. Park, D. Akinwande, and Y. H. Lee, “Recent development of two-dimensional transition metal dichalcogenides and their applications,” Mater. Today, vol. 20, no. 3, pp. 116–130, 2017.

[2] A. T. Hanbicki, M. Currie, G. Kioseoglou, A. L. Friedman, and B. T. Jonker, “Measurement of high exciton binding energy in the monolayer transition-metal dichalcogenides WS2 and WSe2,” Solid State Commun., vol. 203, pp. 16–20, 2015.

[3] A. Chernikov et al., “Exciton binding energy and nonhydrogenic Rydberg series in monolayer WS 2,” Physical review letters, vol. 113, no. 7. p. 076802, 2014.

[4] F. Cadiz et al., “Excitonic linewidth approaching the homogeneous limit in MoS 2-based van der Waals heterostructures,” Phys. Rev. X, vol. 7, no. 2, p. 021026, 2017.

[5] A. A. Shubnic, R. G. Polozkov, I. A. Shelykh, and I. V. Iorsh, “High refractive index and extreme biaxial optical anisotropy of rhenium diselenide for applications in all-dielectric nanophotonics,” Nanophotonics, vol. 9, no. 16. pp. 4737–4742, 2020.

[6] C.-H. Ho and Z.-Z. Liu, “Complete-series excitonic dipole emissions in few layer ReS2 and ReSe2 observed by polarized photoluminescence spectroscopy,” Nano Energy, vol. 56. pp. 641–650, 2019.

[7] A. Arora et al., “Highly anisotropic in-plane excitons in atomically thin and bulklike 1 T′-ReSe2,” Nano Lett., vol. 17, no. 5, pp. 3202–3207, 2017.

[8] R. Gogna, L. Zhang, and H. Deng, “Self-Hybridized, Polarized Polaritons in ReS2 Crystals,” ACS Photonics, vol. 7, no. 12. pp. 3328–3332, 2020.

[9] D. Chakrabarty et al., “Interfacial anisotropic exciton-polariton manifolds in ReS 2,” Optica, vol. 8, no. 11. pp. 1488–1494, 2021.

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