A Spanish team led from the Autonomous University of Madrid (UAM) has observed the formation of a new quantum state in ultrathin materials by cooling a Mott insulator below 11 Kelvin. This finding, published in Nature Communications, could revolutionize the development of superconductors and next-generation electronic devices, marking a milestone in materials science.
A team of researchers from the Autonomous University of Madrid (UAM), IFIMAC, IMDEA Nanoscience and the University of Calabria has studied a type of material known as Mott insulator, characterized because the electrons inside it cannot move due to strong interactions. Surprisingly, when this material is cooled to temperatures below 11 Kelvin (-262.15 °C), the electrons start to move freely, due to the appearance of a new quantum state called "Kondo lattice".
These results, published in Nature Communications, bring us closer to a new generation of quantum technologies that will transform key sectors, from renewable energy to advanced computing.
"Specifically, this discovery expands our understanding of the physics of systems that may enable revolutionary applications in the design of high-temperature superconductors, quantum computing devices, and low-power electronic systems," the authors stress.
New approach to quantum materials design
The study shows how to control electron behavior in two-dimensional systems by stacking two-dimensional materials with different properties. This result shows the way for the design of materials with customized electronic properties, such as superconductivity.
Two-dimensional materials are known for their sensitivity to small changes in the environment, which allows them to transform their properties in a controlled manner. "This work demonstrates how small modifications can drastically change the properties of a material, from an insulator to a conductor or even a superconductor," the authors note.
To illustrate how seemingly simple interactions can generate complex quantum states, the scientists compare Mott’s insulators to a crowded room. In such a space, density prevents free motion, as it does for electrons in these materials.
Kondo shielding, on the other hand, can be likened to the presence of a beginner dancer (magnetic impurity) in a group of experienced dancers (substrate electrons). The presence of the beginner presents an obstacle to the more fluid movements of the experienced ones. When there are many beginner dancers distributed among the experienced dancers, their presence modifies the collective behavior of the dancers, creating a complex dance, different from the one initially planned.
In the case of the Kondo effect, interactions between electrons and magnetic impurities cause the electrons to change their behavior, resulting in an increase in resistance at low temperatures. When the impurities are arranged periodically, the electrons interacting with the various impurities overlap coherently. This modifies the properties of the material at the quantum level, generating a collective state that alters its conductivity in a manner similar to the transformation of choreography.
The researchers combined a two-dimensional Mott insulator with a metallic substrate and investigated its behavior at different temperatures. The team used state-of-the-art techniques, such as tunnel effect microscopy and spectroscopy (STM STS), to analyze the electronic properties of the system at the atomic scale. In addition, they performed simulations based on density functional theory (DFT) to interpret the observed quantum effects.
These methods have allowed us to discover how electrons, initially immobilized in the Mott insulator, manage to delocalize and move freely. Thus, this study not only expands our knowledge of quantum physics, but also underlines the importance of interdisciplinary approaches in the creation of materials with innovative properties.
Bibliographic reference:
Ayani, C. G., Pisarra, M., Ibarburu, I. M. et al. Electron delocalization in a 2D Mott Ayani, C. G., Pisarra, M., Ibarburu, I. M., Rebanal, C., Garnica, M., Calleja, F., Martín, F., & Vázquez de Parga, A. L. (2024). Electron delocalization in a 2D Mott insulator. Nature Communications, 15, 10272. https://doi.org/10.1038/s41467-024-54747-4. https://doi.org/10.1038/s41467-024-54747-4
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