SEOUL, March 20 (AJP) - A research team at Sookmyung Women's University in South Korea has uncovered a new physical mechanism that allows scientists to observe "interlayer excitons" in two-dimensional semiconductors using electric fields. Led by School of Intelligent Electronic Systems Professor Cha Soon-young, the study provides a theoretical framework for a phenomenon that had previously been difficult to explain.
Two-dimensional semiconductors are key materials for the development of next-generation optoelectronic devices and quantum information technology. In a two-layer structure, an interlayer exciton forms when an electron and a hole—a quasiparticle representing the absence of an electron—are located in different layers.
While these excitons have long lifespans and energy levels that can be controlled by external fields, they are notoriously difficult to observe. Because the electron and hole are physically separated, their interaction with light is extremely weak, often leaving them in an invisible "dark" state.
The researchers applied electric fields to bilayer tungsten diselenide (WSe2) and precisely measured its optical spectrum. They discovered that as the electric field increased, the normally undetectable interlayer exciton signals grew progressively stronger.
Earlier studies attributed this brightness to "exciton hybridization," a process where different exciton states mix together. However, Professor Cha's team determined that hybridization alone could not account for their experimental data.
Using an analysis that combined density functional theory (DFT) calculations with exciton modeling, the team proposed a "hole transfer" mechanism. When an electric field is applied, the wave function of the hole in one layer moves partially to the other, creating a quantum superposition state.
This process amplifies the exciton's interaction with light, essentially turning the dark state into a "bright" state. The team's calculations confirmed that this hole transfer mechanism is the primary reason for the increased signal strength, while the contribution from hybridization is significantly smaller.
"This research shows that the optical properties of interlayer excitons are determined by the quantum superposition of charge wave functions rather than simple state mixing," Cha Soon-young said. "These findings provide a critical foundation for future research into quantum physics and the design of 2D semiconductor-based devices."
The study was a collaborative effort with researchers from the University of California, Riverside, Carnegie Mellon University, Nanjing University, National Cheng Kung University, and the National Institute for Materials Science (NIMS) in Japan. The findings were published on March 6, 2026, in Physical Review Letters, a journal ranked in the top 7.5 percent of the physics field.
(Reference Information)
Journal/Source: Physical Review Letters
Title: Brightening interlayer excitons by electric-field-driven hole transfer in bilayer WSe2
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