4 December 2025

Uncovering a new frontier in quantum many-body physics

A team of researchers led by the group of Prof. Jonathan Finley at the Technical University of Munich and MCQST has discovered an unusually large and surprising particle-like state inside an atomically thin semiconductor made of WSe₂. This state, a type of exciton, is created when an electron and a positively charged “hole”, the lack of an electron, bind to each other, forming a short-lived, atom-like state. Typically, excitons involve just one electron and one hole, but when more free electrons are around, the exciton can bind to more than one, forming a larger quantum many-body quasiparticle. In their recent study published in Nature Communications, the team surprisingly uncovered an exciton consisting of as many as twenty bodies, which challenges the current understanding of light interactions with dense two-dimensional electron gases.

Excitons can bind free electrons with distinguishable quantum numbers, creating larger many-body excitations. The researchers were able to track the emergence and evolution of such excitations by electrostatically tuning the electron density in the WSe₂ monolayer. At the highest doping levels, which were achieved for the first time, the team detected the new exciton, involving twenty distinguishable quasiparticles. What makes this finding so unexpected is that theory predicts that in a material with very high electron density, excitons should break apart: the surrounding electrons normally “Coulomb screen”, or weaken, the attraction needed to keep an exciton together.

“These observations were a surprise,” the authors Dr. Alain Djikstra and Amine Ben Mhenni of the Walter Schottky Institute explain. “Mott theory predicts that excitons cannot exist in ultra-dense two-dimensional electron gases, since the exciton size becomes comparable to the screening length. The observation of this new exciton shows that correlations in two-dimensional materials are still not completely understood.” The discovery opens a new frontier in quantum many-body physics, enabling researchers to probe the limits of exciton formation and understand how Coulomb interactions are screened in two-dimensional materials.

Publication

Ten-valley excitonic complexes in charge-tunable monolayer WSe2
Dijkstra, A., Ben Mhenni, A., Van Tuan, D. et al. . Nat Commun 16, 9743 (2025).
DOI: doi.org/10.1038/s41467-025-65731-x

Contact

Dr. Alain Djikstra
Postdoc (EU Marie Curie Fellow)
WSI-TUM
alain.djikstra@wsi.tum.de

Amine Ben Mhenni
Phd Candidate
WSI-TUM
Amine.Ben-Mhenni@wsi.tum.de