Evidence of the polaronic character of excitons in a two-dimensional ferromagnet*

Studies of exciton dynamics in two-dimensional (2D) transition metal dichalcogenide (TMDC) semiconductors have led to discoveries of a variety of fascinating properties for optoelectronic applications. It has been known that exciton dynamics can be strongly affected by lattice vibrations through electron-phonon (e-ph) coupling. The recently discovered 2D ferromagnetic semiconductor, CrI₃, provides a new platform to explore exciton physics beyond the well-studied 2D TMDC semiconductors because of its localized orbitals, intrinsic long-range ferromagnetic order, and strong e-ph coupling. Here we use linear absorption spectroscopy to identify the exciton resonance transitions in bilayer CrI₃. We further use resonant micro-Raman spectroscopy to explore the electron-phonon coupling in bilayer CrI₃. Temperature and magnetic field dependence of e-ph coupling in bilayer CrI₃ will be discussed.