A team of scientists has developed a new method to manipulate quantum materials using excitons, bypassing the need for intense lasers. This approach, led by the Okinawa Institute of Science and Technology and Stanford University, achieves strong Floquet effects with far less energy, reducing the risk of damaging materials. The findings, published in Nature Physics, open pathways to advanced quantum devices.
Scientists have long explored Floquet engineering, a technique that uses periodic influences like light to temporarily alter the electronic properties of materials. Proposed in 2009 by Oka and Aoki, this field has faced challenges due to the need for extremely intense light, which often damages samples and yields only short-lived effects.
Now, researchers from the Okinawa Institute of Science and Technology (OIST), Stanford University, and collaborators have demonstrated a more efficient alternative: excitonic Floquet engineering. Excitons, which are short-lived pairs of electrons and holes formed in semiconductors, interact strongly with the material due to Coulomb forces, especially in two-dimensional structures. "Excitons couple much stronger to the material than photons due to the strong Coulomb interaction, particularly in 2D materials," explained Professor Keshav Dani from OIST's Femtosecond Spectroscopy Unit. This allows for powerful quantum modifications without the destructive high energies of traditional light-based methods.
The team used time- and angle-resolved photoemission spectroscopy (TR-ARPES) on an atomically thin semiconductor. They first applied a strong optical drive to observe standard Floquet behavior, then reduced the light intensity by over an order of magnitude and measured responses 200 femtoseconds later to isolate excitonic effects. "It took us tens of hours of data acquisition to observe Floquet replicas with light, but only around two to achieve excitonic Floquet - and with a much stronger effect," said Dr. Vivek Pareek, now at the California Institute of Technology.
Xing Zhu, a PhD student at OIST, noted that light couples weakly to matter, requiring femtosecond-scale frequencies that risk vaporizing the material. In contrast, excitons, generated from the material's own electrons, provide tunable, self-oscillating energy at lower intensities. Co-author Professor Gianluca Stefanucci from the University of Rome Tor Vergata added that creating a dense population of excitons needs significantly less light, enabling effective periodic drives for hybridization.
This breakthrough extends Floquet effects beyond photons to other bosonic particles like phonons or plasmons, paving the way for practical quantum material design. "We've opened the gates to applied Floquet physics to a wide variety of bosons," concluded Dr. David Bacon, now at University College London. The study appears in Nature Physics (2026, DOI: 10.1038/s41567-025-03132-z).
