Quantum 'alchemy' Made Feasible With Excitons
Okinawa Institute of Science and Technology Graduate University
Imagine a world where materials can be transformed by simply shining a light on them. This concept, once confined to the realms of science fiction and alchemy, is now a tangible reality for physicists exploring the emerging field of Floquet engineering. With a periodic drive, like light, scientists can manipulate the electronic structure of materials, altering their fundamental properties. For instance, a simple semiconductor can be turned into a superconductor.
While the theory of Floquet physics has been around since a groundbreaking proposal by Oka and Aoki in 2009, only a handful of experiments in the past decade have successfully demonstrated Floquet effects. However, these experiments have been limited by the reliance on light, which requires extremely high intensities that can damage the material while only achieving moderate results. But now, a diverse team of researchers from around the world, co-led by the Okinawa Institute of Science and Technology (OIST) and Stanford University, has introduced a revolutionary approach to Floquet engineering. They have shown that excitons can produce Floquet effects much more efficiently than light.
Excitons, formed in semiconductors when individual electrons are excited, carry self-oscillating energy that impacts surrounding electrons in the material at tunable frequencies. Because excitons are created from the material's own electrons, they couple more strongly with the material than light. This discovery opens up a new pathway to the exotic future quantum devices and materials that Floquet engineering promises.
The team used a world-class TR-ARPES (time- and angle-resolved photoemission spectroscopy) setup at OIST to investigate excitonic Floquet effects. By exciting an atomically thin semiconductor with an optical drive and recording electron energy levels, they were able to observe Floquet effects directly. The experiments demonstrated that excitonic Floquet effects can be achieved with significantly lower intensities than optical methods, making the process more practical and less damaging to materials.
This breakthrough is the culmination of OIST's history of exciton research and the world-class TR-ARPES setup they have built. The team has conclusively proven that Floquet effects can be reliably generated with other bosons besides photons, which have dominated the field until now. Excitonic Floquet engineering is significantly less energetic than optical methods, and theoretically, the same effect should be achievable with other types of bosons created through various excitation methods.
This development lays the foundation for practical Floquet engineering, offering great promise for the reliable creation of novel quantum materials and devices. The researchers have opened the gates to applied Floquet physics, inviting a wide variety of bosons. While the recipe for this is still being developed, the spectral signature necessary for the first practical steps has been identified. This is an exciting development, given the strong potential for creating and directly manipulating quantum materials.
