Meet Fractional Excitons - A New Quantum Particle

By Taha KhanReviewed by Louis CastelJan 21 2025

Image Credit: Jurik Peter/Shutterstock.com

What Are Fractional Excitons?

Excitons are quantum states that form due to the interaction between an electron and a hole within semiconductors and insulators. The electron and hole are bound together by Coulomb interaction that depends on material properties and the surrounding dielectric environment. ^{2, 3}

Fractional excitons are a distinct class of excitonic states with unique properties compared to conventional excitons. These quantum particles arise in systems exhibiting fractional quantum Hall (FQH) states, where they behave as neutral particle-hole pairs under specific conditions, such as effective magnetic fields.

Fractional excitons exhibit fractionalization, where quantum properties such as charge or spin are divided into fractional values, providing a deeper understanding of quantum systems and their non-conventional anyonic statistics. ^{4, 5} Theoretical studies place fractional excitons within the framework of systems exhibiting topological order, particularly in FQH effects. Depending on the system's properties, fractional excitons may exhibit bosonic or fermionic behavior. ⁶

The Method Behind the Discovery

The research team at Brown University and the National Institute for Materials Science provided experimental evidence of fractional excitons for the very first time. These excitons exhibit unconventional quantum statistics (fermionic or anyonic), revealing two novel quantum phases: a fractional analog of an exciton condensate and a phase with unique non-bosonic behavior.

The research team conducted their experiments using a Corbino geometry setup that eliminates edge effects in quantum measurements. They constructed the experimental system with a graphene bilayer and graphite gate electrodes that control charge carrier density in each layer. The two graphene layers were separated by 4.5 nm to enable interlayer interactions.

The experimental method used three measurement configurations: parallel flow measurements for charge gaps, counterflow measurements for interlayer correlations, and drag measurements for excitonic pairing. The measurements were conducted at 20 mK with magnetic fields controlling Landau level filling. The team used gate voltages to adjust carrier densities in each layer independently.

The graphene bilayer structure proved effective for studying quantum Hall effects and interlayer interaction. Researchers found that the Corbino geometry allowed clear measurements of bulk properties and interlayer correlations by removing edge channel effects. The setup enabled researchers to examine the relationships between different fractional exciton states under varying conditions. ¹

Implications for Quantum Science

Fractional excitons challenge traditional models by revealing complex electron behaviors under strong magnetic fields, which has profound implications for understanding how particles interact in unconventional quantum systems. This research helps deepen the theoretical foundation of quantum physics, particularly in systems where particle behavior deviates from classical expectations.

The study of fractional excitons also presents an opportunity to refine or expand current quantum field theories. The current quantum field theories may need to be adjusted or extended to accommodate new states of matter that were previously not predicted.

Moreover, exploring the tunability of excitons in two-dimensional semiconductors can help refine the understanding of quasiparticles, exciton binding energies, and bandgaps, which are essential for developing more accurate models of quantum fields. ^{6, 7}

Similarly, these materials exhibit unique quantum phases and interactions that are difficult to observe in higher-dimensional systems, providing researchers with a novel platform to explore quantum phenomena. For instance, the reduced dimensionality in systems like graphene or twisted MoTe₂ enhances the tunability of quantum properties, making it possible to isolate and study the behavior of fractional excitons in environments where conventional quantum effects might not manifest. This provides an opportunity to advance condensed matter physics by investigating new quantum phases and interactions that may lead to next-generation quantum materials development. ^{6, 8}

Impact on Quantum Technology

Fractional excitons can advance quantum computing and communication systems through tunable exciton binding energies and coherent control mechanisms. These properties enable more efficient approaches to quantum bit storage and transmission in two-dimensional materials. ^{9, 10} In controlled environments, such as fractional quantum Hall states, these particles have shown potential for improving quantum computing applications. ⁷

Additionally, leveraging fractional statistics may lead to ultra-efficient devices with reduced decoherence and enhanced stability by stabilizing quantum states against environmental disturbances. ¹¹ These advances could significantly improve the performance and efficiency of quantum technologies.

Research into fractional excitons enhances our understanding of quantum information processing by offering novel approaches to quantum state manipulation. For instance, the fractional Schrödinger equation (FSE) can lead to fractionally enhanced quantum tunneling, enabling more efficient state manipulation and faster quantum computations. ¹² Moreover, unitary fractional-order derivative operators provide a new framework for controlling qubit measurement probabilities, which can optimize quantum interference circuits and improve the performance of quantum algorithms. ¹³ These findings can aid in developing quantum processors capable of utilizing fractional states for computation and storage.

Interested in other particles? Read about neutrinos here

References

1. N. J., Nguyen, R. Q., Batra, N., Liu, X., Watanabe, K., Taniguchi, T., ... & Li, J. I. A. (2025). Excitons in the fractional quantum Hall effect. Nature. https://doi.org/10.1038/s41586-024-08274-3
2. Som, S. (2024). Bose Einstein Condensation of Excitons and Polaritons. Bentham Science Publishers. https://doi.org/10.2174/9789815165401124010004
3. Jankowski, W. J., Thompson, J. J., Monserrat, B., & Slager, R. J. (2024). Excitonic topology and quantum geometry in organic semiconductors. arXiv preprint. https://doi.org/10.48550/arxiv.2406.11951
4. Kwan, Y. H., Hu, Y., Simon, S. H., & Parameswaran, S. A. (2022). Excitonic fractional quantum Hall hierarchy in moiré heterostructures. Physical Review B. https://doi.org/10.1103/PhysRevB.105.235121
5. Morel, T., Lee, J. Y. M., Sim, H. S., & Mora, C. (2022). Fractionalization and anyonic statistics in the integer quantum Hall collider. Physical Review. https://doi.org/10.1103/PhysRevB.105.075433
6. Pichler, F., Kadow, W., Kuhlenkamp, C., & Knap, M. (2024). Single-particle spectral function of fractional quantum anomalous Hall states. arXiv preprint. https://doi.org/10.48550/arxiv.2410.07319
7. Greiter, M., & Wilczek, F. (2024). Fractional Statistics. Annual Review of Condensed Matter Physics. https://doi.org/10.1146/annurev-conmatphys-040423-014045
8. Sharma, L., Rodriguez-Fernandez, C., & Caglayan, H. (2024). Fractional Dimensional Approach to Dielectric Tuning Effects on Excitonic Parameters in 2D semiconductor materials. arXiv preprint. https://doi.org/10.48550/arxiv.2403.11579
9. Purz, T. L., Martin, E. W., Hipsley, B. T., & Cundiff, S. T. (2024). Imaging exciton interactions in two-dimensional materials and heterostructures with spectroscopic microscopy. Journal of Physics D: Applied Physics. https://doi.org/10.1088/1361-6463/ad82f6
10. Sharma, L., Rodriguez-Fernandez, C., & Caglayan, H. (2024). Fractional Dimensional Approach to Dielectric Tuning Effects on Excitonic Parameters in 2D semiconductor materials. arXiv preprint. https://doi.org/10.48550/arxiv.2403.11579
11. Jon, Magne, Leinaas., Jan, Myrheim. (2024). Fractional statistics in low-dimensional systems. https://doi.org/10.1016/b978-0-323-90800-9.00187-6
12. Lewis, J. M., & Carr, L. D. (2024). Exploring Multiscale Quantum Media: High-Precision Efficient Numerical Solution of the Fractional Schrodinger equation, Eigenfunctions with Physical Potentials, and Fractionally-Enhanced Quantum Tunneling. arXiv preprint.   https://doi.org/10.48550/arxiv.2403.07233
13. Alagoz, B. B., & Alagoz, S. (2022). Unitary fractional-order derivative operators for quantum computation. In Fractional-Order Design (pp. 301-336). Academic Press. https://doi.org/10.1016/b978-0-32-390090-4.00016-0

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