Researchers have developed a new method to create hybrid states of matter in lead halide perovskite films at room temperature, a feat typically requiring extreme cold. By fabricating precisely sized nanoscale slots in a thin gold layer, a team from Rice University and their collaborators have managed to merge light with atomic vibrations in the perovskite material, opening new pathways for controlling its energy-harvesting and light-emitting properties. The discovery, detailed in Nature Communications, provides a powerful tool for engineering the quantum behavior of materials used in next-generation solar cells, LEDs, and other optical devices.
The breakthrough hinges on forcing a strong interaction between light and phonons, which are collective, unison vibrations of atoms in a crystalline solid. These vibrations are fundamental to how energy and heat move through a material. By achieving a state known as “ultrastrong coupling,” the scientists were able to create entirely new quantum states called phonon-polaritons, a hybrid of light and matter. This achievement at ambient temperatures is significant because thermal energy usually disrupts such delicate quantum phenomena, relegating most similar experiments to cryogenic conditions. The new technique offers a way to circumvent this limitation, making the exploration and application of these exotic states more practical.
Overcoming Thermal Interference
A primary obstacle in the field of quantum materials is environmental heat. The formation of coherent macroscopic quantum states, where particles or energy waves act in unison, is essential for applications like superconductivity and quantum computing. However, at room temperature, random thermal agitations typically cause “dephasing,” a process where this collective behavior is quickly lost. This is why many quantum effects, such as Bose-Einstein condensation and superradiance, have historically been observed only at temperatures close to absolute zero. The ability to generate and sustain these states under normal conditions is therefore a major goal for materials scientists.
Perovskite materials have shown surprising resilience against this dephasing, making them a promising platform for room-temperature quantum applications. Some research suggests that the formation of large polarons in hybrid perovskites can provide a form of “quantum analogue of vibration isolation,” which shields electronic excitations from thermal noise. The work by the Rice University team builds on this inherent potential of perovskites, but uses a novel structural engineering approach to induce a specific and powerful light-matter interaction rather than relying solely on the material’s intrinsic properties. This allows for a more direct and tunable method of creating desired quantum states.
A Precision Engineering Approach
To manipulate the perovskite’s properties, the researchers engineered a specialized surface to interact with it. They did not use conventional methods like high-power lasers, instead opting for a passive but highly effective fabrication technique. This involved creating an array of tiny, parallel slots in a thin film of gold, upon which the lead halide perovskite film was deposited.
Trapping Light with Nanoslots
The core of the technique lies in the geometry of these nanoscale slots. Each slot is incredibly small, approximately a thousand times thinner than a sheet of plastic wrap, and designed to function as a miniature metallic trap for light. When light in the terahertz frequency range passes through, these slots resonate and confine the light’s energy, effectively tuning its frequency. This confinement is crucial for amplifying the interaction between the light and the perovskite material layered on top. The precise frequency of the trapped light is determined by the physical dimensions of the slots.
Tuning for Resonance
The researchers fabricated arrays with seven different slot lengths. Longer slots were designed to trap lower-frequency light, while shorter ones trapped higher frequencies. This systematic variation allowed the team to finely tune the confined light’s frequency to precisely match the natural vibration frequencies of two specific phonons within the perovskite crystal. By aligning these frequencies, they could drive the system into a regime of exceptionally strong interaction, a condition necessary for the light and phonons to merge their identities.
The Emergence of Hybrid Matter
The successful alignment of light and phonon frequencies pushed the system into a state of “ultrastrong coupling.” This is not a simple interaction but a condition where the coupling becomes so strong that the original states of light and matter are no longer distinguishable. Instead, they combine to form new, hybrid quantum states. According to Dasom Kim, a Rice doctoral alumnus and first author of the study, this was the first time two distinct phonons in a perovskite thin film have been brought into this ultrastrong coupling regime at room temperature using a single engineered terahertz resonance.
The result was the formation of three distinct types of phonon-polaritons. Each of these is a unique blend of light and atomic vibration, possessing properties of both. The strength of this interaction was remarkably high, with the coupling ratio reaching about 30% of the phonon’s own frequency. This powerful, controllable hybridization of matter and light at ambient conditions represents a significant step forward in quantum state engineering.
New Frontiers for Perovskite Technology
This discovery provides scientists with a powerful new lever for manipulating how perovskite materials absorb, transport, and emit energy. The ability to create hybrid light-matter states on demand could lead to the development of more sophisticated and efficient optoelectronic devices. Because phonons play a central role in how materials handle energy, controlling them directly could improve the performance of solar cells by guiding energy flow more effectively and reducing heat loss. In LEDs, it could enable more precise control over light emission properties.
Beyond existing technologies, this work paves the way for new device concepts built on engineered quantum states. The tunability of the nanoslot platform means that materials can be designed to have specific, tailored interactions with light. This could prove valuable for creating specialized sensors or new types of lasers. Furthermore, related research has demonstrated that perovskite thin films can be synthesized on large, flexible substrates, suggesting a potential route for fabricating scalable and adaptable devices based on these quantum principles. As researchers continue to explore the “good, the bad, and the ugly” aspects of nanoscale properties in perovskites, the ability to deliberately engineer quantum states offers a promising path to enhancing their performance and stability.