CAREER: Probing exciton-exciton correlations and phase transitions for spin-polarized excitons in monolayer transition metal dichalcogenides

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This award is funded in whole or in part under the American Rescue Plan Act of 2021 (Public Law 117-2). Non-technical abstract When light is absorbed by a solid, it can create a transient excitation quasiparticle, the so-called exciton, which carries information from both the light and the matter. Understanding excitonic interactions are crucial for the future design of quantum devices with contact-free, all-optical control and sensing. This project investigates the quantum correlations between excitons in an atomically-thin two-dimensional crystal with exceptionally strong light-matter interactions. The unique optical and electronic properties of the two-dimensional crystal promise the realization of quantum correlation well above the liquid helium temperature. The research results will establish new platform systems to achieve on-chip operation and control of coherence for future quantum technology developments. Integrated with the research, the project aims to promote the participation of women in STEM and train the next-generation STEM workforce through interdisciplinary research projects and tasks. A series of career support seminars for women in STEM will be organized at the University of Florida. In addition, optics science demonstration stations will be developed for display in a local museum to increase STEM awareness in a younger generation.This project is jointly funded by the Condensed Matter Physics (CMP) and the Electronic and Photonic Materials (EPM) programs of the Division of Materials Research (DMR).Technical abstract An exciton is a bound electron-hole pair that can be considered as a Boson, often created through optical excitations in semiconductors. Beyond the dilute exciton gas limit, exciton-exciton correlation forms, and the possibility of achieving quantum degeneracy of exciton liquid and condensate phases have attracted great attention for decades. The recent advent of two-dimensional (2D) semiconductors of transition metal dichalcogenides provides a completely new paradigm for exciton physics, where excitons have anomalously strong binding energy and enable all-optical control of the spin and valley degrees of freedom. This project aims to investigate the nonlinear exciton interactions and seek experimental signatures of exciton complex correlations in tungsten-based monolayer transition metal dichalcogenides. In particular, this research will focus on spin-polarized excitonic states, which have long lifetimes and support a high exciton density. Both the classical regime and the possible quantum degeneracy of 2D excitons will be investigated through a combination of ultrafast optical spectroscopies and optoelectronic probes. The outcome will inform our understanding of excitonic many-body interactions in 2D and lay the foundation for realizing macroscopic coherence in compact 2D devices. Investigation of these spin-polarized excitons will also elucidate how the spin polarization of bosons affects the formation of correlation and further macroscopic coherence.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.