New States in 2D Materials

Thin two-dimensional (2D) materials can exhibit excitonic properties, making them an attractive platform to explore polaritonic physics.

Donghai Li and a group of researchers from Julius-Maximilians-Universität (JMU) Würzburg in Bavaria, Germany, discovered that placing 2D semiconductors in microcavities can lead to a strong interaction between not just excitons and cavity photons but also with phonons. This may shift the paradigm of exciton-polariton physics in 2D materials by highlighting and quantifying the role of phonons therein.

The researchers developed a novel method of coherent 2D micro-spectroscopy, providing spectral resolution for both the excitation and detection steps in combination with microscopic spatial resolution and 20 femtosecond temporal resolution. In this case, a rich multipeak spectrum of excitations is mapped. Comparison with a novel vibronic polariton model that considers the degree of freedom of excitons and photons and phonons reveals multiple polariton branches induced by exciton-photon-phonon hybridization.

This discovery of unobserved bright states in microcavities with embedded 2D materials is potentially important for realizing room-temperature Bose-Einstein condensation and polariton lasing in these systems.