[Paper Review] Ultrastrong Light-Matter Coupling in 2D Metal-Chalcogenates

Surendra B. Anantharaman, Jason Lynch+11 more|arXiv (Cornell University)|Aug 22, 2023

Strong Light-Matter Interactions4 citations

TL;DR

This study demonstrates ultrastrong light-matter coupling in two-dimensional metal-chalcogenate (MOCHA) crystals, specifically mithrene, achieving Rabi splittings exceeding 600 meV at room temperature due to strong excitonic oscillator strength and high refractive index. The system exhibits bright polariton emission and linewidth narrowing to ~1 nm in closed Fabry-Perot cavities, establishing MOCHA materials as promising for deep green-blue polaritonics.

ABSTRACT

Hybridization of excitons with photons to form hybrid quasiparticles, exciton-polaritons (EPs), has been widely investigated in a range of semiconductor material systems coupled to photonic cavities. Self-hybridization occurs when the semiconductor itself can serve as the photonic cavity medium resulting in strongly-coupled EPs with Rabi splitting energies > 200 meV at room temperatures which recently were observed in layered two-dimensional (2D) excitonic materials. Here, we report an extreme version of this phenomenon, an ultrastrong EP coupling, in a nascent, 2D excitonic system, the metal organic chalcogenate (MOCHA) compound named mithrene. The resulting self-hybridized EPs in mithrene crystals placed on Au substrates show Rabi Splitting in the ultrastrong coupling range (> 600 meV) due to the strong oscillator strength of the excitons concurrent with the large refractive indices of mithrene. We further show bright EP emission at room temperature as well as EP dispersions at low-temperatures. Importantly, we find lower EP emission linewidth narrowing to ~1 nm when mithrene crystals are placed in closed Fabry-Perot cavities. Our results suggest that MOCHA materials are ideal for polaritonics in the deep green-blue part of the spectrum where strong excitonic materials with large optical constants are notably scarce.

Motivation & Objective

• To explore ultrastrong light-matter coupling in emerging 2D metal-chalcogenate (MOCHA) materials, particularly mithrene.
• To address the scarcity of strong excitonic materials with large optical constants in the deep green-blue spectral range.
• To demonstrate self-hybridized exciton-polaritons with high Rabi splitting and bright emission at room temperature.
• To investigate polariton dispersion and linewidth engineering in mithrene-based heterostructures.

Proposed method

• Fabrication of monolayer mithrene crystals on gold substrates to enable self-hybridization of excitons with cavity modes.
• Measurement of Rabi splitting via photoluminescence spectroscopy to quantify light-matter coupling strength.
• Use of closed Fabry-Perot cavities to confine light and enhance polariton quality, reducing emission linewidth.
• Low-temperature measurements to probe polariton dispersion and many-body effects.
• Analysis of optical constants and excitonic oscillator strength to explain ultrastrong coupling.

Experimental results

Research questions

• RQ1 Can ultrastrong light-matter coupling (Rabi splitting > 600 meV) be achieved in a 2D metal-chalcogenate system like mithrene?
• RQ2 What role do the high refractive index and strong oscillator strength of mithrene play in enabling ultrastrong coupling?
• RQ3 Can bright, room-temperature polariton emission be achieved in MOCHA-based heterostructures?
• RQ4 How does cavity confinement affect polariton linewidth and emission quality in mithrene?
• RQ5 What is the nature of polariton dispersion in mithrene at low temperatures?

Key findings

• Rabi splitting in mithrene exceeds 600 meV, placing the system in the ultrastrong coupling regime.
• Bright exciton-polariton emission is observed at room temperature due to strong oscillator strength and high refractive index.
• In closed Fabry-Perot cavities, the polariton emission linewidth narrows to approximately 1 nm.
• Low-temperature measurements reveal well-defined polariton dispersion relations.
• The combination of strong excitonic response and high optical constants in mithrene enables efficient self-hybridization without external cavities.