Imagine electronic devices that never overheat and sensors that detect pollutants with unmatched precision.
Researchers at CUNY ASRC have taken a major step toward making this a reality by discovering how to generate long-wave infrared and terahertz waves more efficiently.
Revolutionizing Electronics with Infrared and Terahertz Waves
Imagine a future where your phone stays cool no matter how long you use it, and built-in sensors can detect harmful chemicals with incredible accuracy. A new study published today (March 19) in Nature introduces a breakthrough method for generating long-wave infrared and terahertz waves, bringing us closer to these possibilities. Led by researchers at the Advanced Science Research Center at the CUNY Graduate Center (CUNY ASRC), this work could lead to smaller, more affordable infrared light sources and improved heat management in electronic devices.
At the heart of this discovery are phonon-polaritons, a special type of electromagnetic wave that forms when light interacts with vibrations in a material’s crystal structure. These waves have remarkable properties: they can focus long-wavelength infrared energy into nanoscale regions and efficiently dissipate heat. This makes them promising for advanced technologies such as high-resolution imaging, molecular sensing, and electronic cooling. However, despite their potential, most research on phonon-polaritons has remained theoretical or confined to lab experiments, with real-world applications still largely unexplored.
The Challenge of Generating Phonon-Polaritons
“One major challenge is that exciting and detecting phonon-polariton waves is both expensive and inefficient, typically involving costly mid-infrared or terahertz lasers and near-field scanning probes,” said corresponding author Qiushi Guo, a professor with the CUNY ASRC’s Photonics Initiative and the CUNY Graduate Center’s Physics program.” We wanted to explore whether we could emit phonon-polaritons using just an electrical current, similar to how semiconductor lasers or LEDs work,” Guo said.
In this study, Guo’s team (in collaboration with researchers from Yale University, California Institute of Technology, Kansas State University, and ETH Zurich) found that the key was selecting the right combination of materials: a thin layer of graphene sandwiched between two hexagonal boron nitride (hBN) slabs.
The Science Behind Hyperbolic Phonon-Polaritons
First, in hBN, phonon-polaritons possess a significantly higher density of states and can propagate within the bulk, behaving like deep-subwavelength light rays that bounce back and forth between material boundaries. These specialized phonon-polaritons are referred to as hyperbolic phonon-polaritons (HPhPs).
Graphene is well known for its high electron mobility at room temperature. When encapsulated by hBN slabs, its mobility is further enhanced due to surface passivation and reduced impurities. “This means that when a current passes through the graphene encapsulated by hBN slabs, electrons in graphene can be accelerated to very high speeds and efficiently scatter with HPhPs in hBN,” Guo explained.
Electrically Induced Phonon-Polaritons: A Game Changer
The idea proved successful in the experiment. Remarkably, the team observed the emission of HPhPs when applying a modest electric field of just 1 V/µm to the graphene, highlighting the efficiency of HPhP electroluminescence. The study provides the first experimental demonstration of exciting phonon polariton waves exclusively through electrical methods.
The study also revealed intriguing physics underlying the HPhP electroluminescence. Specifically, the team identified two possible pathways for HPhP emission. “When the electron concentration in graphene is low, HPhPs are emitted through interband transitions. However, at higher electron concentrations, HPhP emission occurs through both interband transitions and intraband Cherenkov radiation in graphene,” said former Caltech postdoc Iliya Esin, now an assistant professor of physics at Bar Ilan University, Israel and a corresponding author of the study.
This discovery not only opens new avenues for developing nanoscale long-wave infrared or terahertz light sources but also presents exciting opportunities for energy applications. During the HPhPs electroluminescence, hot electrons in graphene rapidly lose their excess kinetic energy—the primary cause of overheating. Harnessing this mechanism can enable efficient heat dissipation in electronic devices, according to Guo.
Paving the Way for Future Technologies
The electrically pumped phonon-polariton light sources open the door to practical, scalable technologies. From next generation molecular sensing to improved heat management in electronics, this innovation lays the foundation for transformative advancements in energy-efficient, compact technologies that could redefine our modern devices.
Reference: “Hyperbolic phonon-polariton electroluminescence in 2D heterostructures” by Qiushi Guo, Iliya Esin, Cheng Li, Chen Chen, Guanyu Han, Song Liu, James H. Edgar, Selina Zhou, Eugene Demler, Gil Refael and Fengnian Xia, 19 March 2025, Nature.
DOI: 10.1038/s41586-025-08686-9
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