At the frontier of materials science, a groundbreaking development has emerged from researchers at Rice University and their collaborators, revealing a revolutionary method for manipulating light and vibrations in lead halide perovskites at room temperature. This pioneering study, recently published in Nature Communications, showcases how intricate nanoscale engineering enables two distinct phonon modes within perovskite thin films to achieve ultrastrong coupling with terahertz-frequency light. The implications of this discovery are profound, opening transformative pathways for enhancing optoelectronic devices, including solar cells and LEDs, by finely tuning their energy transport and emission characteristics.
Phonons, the quantized collective vibrations of atoms within crystalline solids, fundamentally govern the movement of heat and energy through materials. They dictate pivotal processes in light-harvesting and emission, making their control a linchpin in next-generation photonic and electronic device engineering. Traditionally, achieving strong interactions between phonons and electromagnetic fields requires extreme conditions or bulky materials. However, this new research circumvents such limitations by leveraging nanoscale metallic architectures, thereby bringing ultrastrong phonon-light coupling into practical, device-compatible realms at ambient conditions.
The crux of the innovation lies in the fabrication of nanoscale slots, carved with precision into thin gold films. These slots, some a thousand times thinner than standard plastic wrap, act as resonant traps that confine terahertz-frequency electromagnetic waves. By meticulously adjusting the slot dimensions—a series of seven different lengths—researchers could match the confined light frequencies precisely with the intrinsic vibration frequencies of the perovskite phonons. This meticulous engineering harnesses a coupling phenomenon known as “ultrastrong coupling,” wherein the interaction strength is so elevated that it fundamentally alters the quantum states of both light and matter.
According to Dr. Dasom Kim, a key contributor and recent doctoral alumnus of Rice, this study represents the inaugural demonstration of two phonon modes in a perovskite thin film concurrently achieving ultrastrong coupling with a singular terahertz resonance at room temperature. The ability to induce and observe such a regime without resorting to high-power laser systems or cryogenic conditions underscores the accessibility and scalability of this approach for future technology integration.
By varying the nanoslot lengths, the team could tune the resonance frequency of the plasmonic modes confined within the gold layer, thereby elegantly controlling the strength and nature of light-phonon interactions. Longer slots corresponded to lower-frequency resonances, while shorter slots trapped higher-frequency light. The resulting hybridization between confined photons and vibrational modes led to the formation of three distinct quantum hybrid states called phonon-polaritons. These hybrid quasiparticles embody a superposition of electromagnetic waves and lattice vibrations, manifesting fundamentally new light-matter behavior.
Remarkably, the coupling ratio—the measure of interaction strength relative to phonon frequency—reached an unprecedented 30% at room temperature. This stands in stark contrast to earlier efforts where such ultrastrong coupling was often limited to single phonon modes or achieved only under cryogenic conditions. The robust interaction observed here sets a new benchmark for manipulating vibrational quantum states in technologically relevant materials.
The experimental observations were rigorously supported by comprehensive numerical simulations and a robust quantum theoretical framework. These models confirmed not only the presence of multimode ultrastrong coupling but also quantified the precise interaction strengths. The theoretical approach accounted for various physical parameters including cavity geometry, material permittivity, and phonon mode dispersions, providing deep insights into the underlying mechanisms driving the phenomenon.
Advances in nanofabrication techniques and the enhanced quality of perovskite thin films were pivotal enablers of these results. The researchers credit these technological strides for allowing the construction of highly engineered nanoslot arrays with remarkable precision and reproducibility. Such advancements facilitate a gentle, device-compatible strategy to manipulate phonon-polaritonic states without the complications of extreme operational environments or complex device architectures.
Professor Junichiro Kono, the study’s senior and corresponding author at Rice, emphasizes the broader significance of this work. By revealing completely new phonon behaviors through tailored nanoscale environments rather than extreme external conditions, they unlock a versatile toolset to steer energy flow in optoelectronic devices. This capability is particularly relevant for improving performance metrics and reducing energy losses in perovskite-based photovoltaics and LEDs, materials already celebrated for their outstanding optoelectronic properties.
The discovery also opens intriguing prospects for quantum technologies, where controlling hybrid light-matter states under ambient conditions is highly sought after. Phonon-polaritons exhibiting ultrastrong coupling could serve as platforms for novel quantum state engineering and information processing, bridging solid-state physics with photonics in unprecedented ways.
This research was generously supported by multiple funding agencies, including the U.S. Army Research Office, the W.M. Keck Foundation, the Gordon and Betty Moore Foundation, and others, reflecting a broad recognition of its transformative potential. Collaborative contributions spanned expertise in experimental physics, quantum theory, materials science, and nanofabrication, illustrating the interdisciplinary nature essential for breakthroughs at the intersection of quantum optics and condensed matter physics.
Looking ahead, the team envisions exploiting the tunable nature of these nanostructured perovskite systems to develop high-efficiency, low-energy optoelectronic devices. By refining slot geometries and material compositions, further customization of phonon-polariton interactions could be realized, paving the way for tailored quantum materials with bespoke functionalities.
In summary, the breakthrough of achieving multimode ultrastrong coupling between phonons and terahertz-frequency light in lead-halide perovskites at room temperature ushers in a new era in quantum materials research. It dramatically expands the toolkit available for controlling the fundamental quantum interactions that govern energy transfer, light harvesting, and emission. As this field rapidly progresses, one can anticipate remarkable innovations that leverage these newly accessible quantum states to redefine the limits of photonic and electronic device performance.
Subject of Research: Multimode phonon-polaritons and ultrastrong coupling phenomena in lead-halide perovskite thin films.
Article Title: Multimode phonon-polaritons in lead-halide perovskites in the ultrastrong coupling regime
News Publication Date: September 30, 2025
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Image Credits: Jorge Vidal/Rice University
Keywords
Phonons, Polaritons, Perovskites, Quantum states, Quantum optics, Quantum matter, Optics, Light, Electromagnetic waves, Quantum mechanics, Research methods, Particle physics, Gold, Technology, Nanotechnology
