Unveiling Polaron Transformation in 2D Tellurene

Researchers led by Shengxi Huang at Rice University investigated the behavior of polarons, a type of quasiparticle, in the nanomaterial tellurene. They found that as tellurene’s thickness decreases to just a few nanometers, its electronic and optical properties undergo significant changes due to transformations in the interaction between polarons and the material's atomic vibrations. The study was published in Science Advances.

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To explain how matter behaves at infinitesimal scales, researchers use singular concepts to represent collective behaviors, similar to labeling synchronized bird flight as a "flock" or "murmuration." These phenomena, referred to as quasiparticles, could play a role in advancing next-generation technologies.

Shengxi Huang is an Associate Professor of Electrical and Computer Engineering and Materials Science and Nanoengineering at Rice.

Tellurene, a nanomaterial first synthesized in 2017, consists of tiny chains of tellurium atoms. It exhibits properties that make it valuable for sensing, electronic, optical, and energy applications.

Tellurene exhibits dramatic changes in its electronic and optical properties when its thickness is reduced to a few nanometers compared to its bulk form. Specifically, these changes alter how electricity flows and how the material vibrates, which we traced back to the transformation of polarons as tellurene becomes thinner.

Kunyan Zhang, Doctoral Alumna and Study First Author, Rice University

A polaron emerges when charge-carrying particles, like electrons, interact with vibrations in a material's atomic or molecular lattice. It’s akin to a phone ringing in a crowded auditorium during a lecture: just as the audience collectively turns their attention to the sound, the lattice vibrations reorient themselves in response to the charge carriers, forming an aura of polarization⎯that gives the quasiparticle its name.

The magnitude of this response, or the extent of the aura, can vary significantly depending on the thickness of the tellurene layer. Understanding this polaron transition is crucial as it shows how fundamental interactions between electrons and lattice vibrations affect material behavior, especially at low dimensions.

“This knowledge could inform the design of advanced technologies like more efficient electronic devices or novel sensors and help us understand the physics of materials at the smallest scales,” said Shengxi Huang, Associate Professor and Corresponding Author from Rice University.

The researchers hypothesized that as tellurene transitions from bulk material to nanometer-scale thicknesses, polarons shift from large, dispersed electron-vibration interactions to smaller, localized interactions. This hypothesis was supported by both calculations and experimental measurements.

We analyzed how the vibration frequencies and linewidths varied with thickness and correlated these with changes in electrical transport properties, complemented by the structural distortions observed in X-ray absorption spectroscopy. Furthermore, we developed a field theory to explain the effects of enhanced electron-vibration coupling in thinner layers.

Kunyan Zhang, Doctoral Alumna and Study First Author, Rice University

Compared to previous studies, the team's comprehensive approach offered a more detailed understanding of the thickness-dependent dynamics of polarons in tellurene. This progress was enabled by the development of high-quality tellurene samples and advancements in sophisticated analytical techniques.

Our findings highlight how polarons impact electrical transport and optical properties in tellurene as it becomes thinner. In thinner layers, polarons localize charge carriers, leading to reduced charge carrier mobility. This phenomenon is crucial for designing modern devices, which are continually becoming smaller and rely on thinner materials for functionality.

Kunyan Zhang, Doctoral Alumna and Study First Author, Rice University

Reduced charge mobility could limit the performance of electronic components, particularly in applications such as high-performance computing or power transmission, where high conductivity is essential. However, this localization effect may provide valuable insights for the design and development of phase-change, ferroelectric, thermoelectric, and quantum devices, as well as high-sensitivity sensors.

Huang said, “Our study provides a foundation for engineering materials like tellurene to balance these trade-offs. It offers valuable insights into designing thinner, more efficient devices while addressing the challenges that arise from the unique behaviors of low-dimensional materials, which is vital for the development of next-generation electronics and sensors.”

The study was funded by the National Science Foundation, the Air Force Office of Scientific Research, the Welch Foundation, and the US Department of Energy.

Journal Reference:

‌Zhang, K., et al. (2025) Thickness-dependent polaron crossover in tellurene. Science Advances. doi.org/10.1126/sciadv.ads4763.