Paper accepted in Physical Review Letters

Our work on the thickness-dependent optical response of the magnetic layered material CrI₃ has been accepted for publication in Physical Review Letters. The study maps how the optical properties of this van der Waals crystal evolve from the monolayer limit to flakes with mesoscale thickness.

Chromium triiodide is a particularly interesting material because its magnetic and electronic behaviour changes as the number of layers is reduced. Understanding its optical response is essential both for interpreting optical experiments and for designing devices that combine magnetism, light and two-dimensional materials. Until now, however, measurements performed at individual wavelengths or on a restricted set of thicknesses offered only a partial view.

The research uses hyperspectral microscopy to obtain spatially resolved optical spectra from CrI₃ flakes containing regions with different thicknesses. This approach makes it possible to follow the evolution of the complex dielectric function continuously, from a single layer to much thicker crystals, while keeping the experimental conditions consistent across the sample.

The results reveal a non-monotonic evolution rather than a simple progression from two-dimensional to bulk behaviour. Several spectral features change in energy and intensity as the number of layers increases, showing that the mesoscale regime has its own optical characteristics. These observations provide a detailed experimental reference for theoretical descriptions of electronic structure, excitonic effects and interlayer coupling in magnetic van der Waals materials.

The work also demonstrates the value of hyperspectral imaging as a quantitative tool for materials research. By combining microscopy with spectroscopy, it connects local morphology and thickness with the complete optical response. The same methodology can be applied to other layered semiconductors, magnetic crystals and heterogeneous samples in which relevant properties vary over micrometre distances.

The study was carried out by M. Galbiati, F. Ramiro-Manzano, J. J. Pérez Grau, F. Cantos-Prieto, J. Meseguer-Sánchez, I. Kosic, F. Mione, A. Pallarés Vilar, A. Cantarero, D. Soriano and E. Navarro-Moratalla.

The complete publication record, abstract, figures and links are available on the research page: Monolayer-to-Mesoscale Modulation of the Optical Properties in 2D CrI₃ Mapped by Hyperspectral Microscopy.