This article has been reviewed according to Science X's editorial process and policies. Editors have highlighted the following attributes while ensuring the content's credibility: A study from the Research Center for Materials Nanoarchitectonics (MANA), one of the centers under the National Institute for Materials Science (NIMS), presents a new method to reveal hidden material disorder reflected in complex photoluminescence spectra, paving the way for new optical diagnostics of material disorder in two-dimensional semiconductors and related light-emitting materials. When two ultrathin semiconductor layers, such as molybdenum diselenide and tungsten diselenide (MoSe2/WSe2), are stacked with a slight twist, they form a repeating pattern called a moiré heterostructure.
These structures have unusual light-emitting properties, featuring a complex landscape of photoluminescence spectra across their surface. While scientists often analyze materials by looking at the individual peaks of their emission spectra, moiré heterostructures produce spectra with many overlapping peaks whose origins are difficult to explain individually. To address this challenge, Katsunori Wakabayashi from MANA has developed a theoretical framework to explain this complexity.
Rather than decomposing spectra peak by peak, his approach examines how simple descriptors, such as peak energy and average energy, change spatially across a sample. The research is published in the journal Physical Review Research. By applying this theoretical framework to descriptor correlations reported for a MoSe2/WSe2 heterostructure, Wakabayashi found that different features respond to different layers of hidden disorder in the material, hinting at a hierarchy of disorder.
The first level corresponds to a smooth "background" that varies over larger distances of a few micrometers. In contrast, the second is finer and much more localized, arising from small defects or exciton-trapping sites in the heterostructure. By comparing how these spectral features vary in space using a detailed theoretical analysis, researchers can mathematically infer the underlying landscape of disorder in the bilayer material without relying on spectral peak decomposition.
Tiny structural imperfections and hidden disorder can strongly affect how materials emit and interact with light. Thus, this new framework hints at a practical way to diagnose material quality issues directly from optical data, without relying on uncertain peak-by-peak spectral assignment. "This work could help researchers make better and more reproducible materials for light-emitting devices, optical sensors and quantum technologies," remarks Wakabayashi.
Katsunori Wakabayashi, Hierarchical disorder in moiré exciton photoluminescence probed by spectral-descriptor correlations, Physical Review Research (2026). DOI: 10.1103/jt25-c8fp Journal information: Physical Review Research Provided by National Institute for Materials Science BSc Life Sciences & Ecology. Microbiology lab background with pharmaceutical news experience in oil, gas, and renewable industries.
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