skip to main content


This content will become publicly available on December 4, 2018

Title: Ligand-field helical luminescence in a 2D ferromagnetic insulator

Bulk chromium tri-iodide (CrI 3) has long been known as a layered van der Waals ferromagnet. However, its monolayer form was only recently isolated and confirmed to be a truly two-dimensional (2D) ferromagnet, providing a new platform for investigating light–matter interactions and magneto-optical phenomena in the atomically thin limit. Here in this paper, we report spontaneous circularly polarized photoluminescence in monolayer CrI 3 under linearly polarized excitation, with helicity determined by the monolayer magnetization direction. In contrast, the bilayer CrI 3 photoluminescence exhibits vanishing circular polarization, supporting the recently uncovered anomalous antiferromagnetic interlayer coupling in CrI 3 bilayers. Distinct from the Wannier–Mott excitons that dominate the optical response in well-known 2D van der Waals semiconductors, our absorption and layer-dependent photoluminescence measurements reveal the importance of ligand-field and charge-transfer transitions to the optoelectronic response of atomically thin CrI 3. We attribute the photoluminescence to a parity-forbidden d–d transition characteristic of Cr 3+ complexes, which displays broad linewidth due to strong vibronic coupling and thickness-independent peak energy due to its localized molecular orbital nature.
 [1] ;  [1] ;  [2] ;  [3] ;  [4] ;  [1] ;  [2] ;  [3] ; ORCiD logo [1] ; ORCiD logo [5] ; ORCiD logo [6] ;  [4] ;  [2] ; ORCiD logo [7]
  1. Univ. of Washington, Seattle, WA (United States). Dept. of Physics
  2. Massachusetts Inst. of Technology (MIT), Cambridge, MA (United States). Dept. of Physics
  3. Washington Univ., St. Louis, MO (United States). Dept. of Physics
  4. Carnegie Mellon Univ., Pittsburgh, PA (United States). Dept. of Physics
  5. Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States). Materials Science & Technology Division
  6. Univ. of Hong Kong (China). Dept. of Physics and Center of Theoretical and Computational Physics
  7. Univ. of Washington, Seattle, WA (United States). Dept. of Physics, and Dept. of Materials Science and Engineering
Publication Date:
Grant/Contract Number:
Accepted Manuscript
Journal Name:
Nature Physics
Additional Journal Information:
Journal Volume: 14; Journal Issue: 3; Journal ID: ISSN 1745-2473
Nature Publishing Group (NPG)
Research Org:
Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States)
Sponsoring Org:
USDOE Office of Science (SC), Basic Energy Sciences (BES) (SC-22)
Country of Publication:
United States
OSTI Identifier: