Researchers from Gwangju Institute of Science and Technology (GIST) in Korea managed to tune the electron–phonon coupling strength in strontium ruthenate by controlling its electronic dimensionality and interlayer distance. This novel method could potentially be applied to synthesize materials with desired coupling strength for advanced applications.
Newswise — The interaction between electrons and phonons, which are the discrete units of crystal vibrations, is a closely intertwined process within crystals. In solid state physics, the strength of this electron-phonon coupling plays a crucial role as a fundamental physical quantity. It governs the electrodynamic behaviors and correlated functionalities exhibited by materials, ultimately leading to intriguing material properties that can be harnessed for advanced applications. However, traditionally, the coupling strength has been regarded as an inherent property of a material, lacking any means of intentional control to tailor it according to specific application requirements.
In a significant breakthrough, Professor Jong Seok Lee and his team at the Gwangju Institute of Science and Technology in Korea have successfully tackled the challenge of controlling the electron-phonon coupling strength. Through their research, they have showcased the remarkable capability to manipulate this coupling by employing synthetic heterostructures composed of transition metal oxides. This achievement has led to a substantial amplification in the strength of the coupling, opening up new possibilities in the field.
The researchers have provided a comprehensive account of their groundbreaking work in a paper published online on April 13, 2023. Their findings have been formally published in Volume 10, Issue 16 of the esteemed Advanced Science journal on June 2, 2023. This remarkable advancement marks a significant milestone in the quest to control and enhance the electron-phonon coupling strength, paving the way for exciting developments and applications in various scientific and technological domains.
Professor Lee explains that the electron-phonon coupling is inherently dictated by the crystal structure of a solid. Therefore, it was of utmost importance to explore novel approaches that could provide a means to manipulate or strengthen this coupling. This served as the driving force behind the researchers' current work, as they sought to overcome the limitations imposed by the intrinsic nature of electron-phonon coupling and unlock new possibilities for controlling and enhancing its strength.
The researchers conducted a study where they showcased the manipulation of electron-phonon coupling strength at the atomic level in synthetic superlattices composed of strontium ruthenate (SRO) and strontium titanate (STO). These superlattices consist of periodic layers of the two materials. The researchers achieved this impressive accomplishment by creating an artificial heterostructure within the SRO/STO system. This involved controlling the electronic dimensionality, adjusting the distance between layers, and enhancing the periodic nature of the synthetic atomic network.
Interestingly, the researchers discovered that reducing the dimensionality of the synthetic SRO/STO superlattices from 3D (bulk) to quasi-2D resulted in an astounding 300-fold increase in the strength of electron-phonon coupling. They attributed this significant enhancement to the non-local nature of the coupling within the superlattices, which becomes particularly pronounced in the 2D electronic state. Furthermore, through temperature-dependent electron-phonon coupling measurements, they observed that the electrons in the 2D SRO layers interacted with optical phonons, which are vibrations capable of absorbing or emitting light. This interaction with optical phonons further contributed to the overall enhancement of the electron-phonon coupling.
The progress made in this study opens up exciting prospects for manipulating and adjusting the strength of electron-phonon coupling in crystals, thereby creating new avenues for engineering applications. Moreover, it offers valuable insights into the nature of quantum materials. Professor Lee, expressing optimism, highlights the significance of electron-phonon coupling not only in the performance of thermoelectric devices but also in the energy-harvesting efficiency of solar cells. Nano-scale devices currently face challenges related to overheating, which adversely affects their performance. Prof. Lee speculates that the findings of this research can potentially address the overheating issue, leading to improved performance of nano-scale devices.
In summary, the research findings shed light on the various mechanisms that can be employed to manipulate the electron-phonon coupling strength in synthetic crystals. This knowledge not only holds promise for technological advancements but also contributes to a better comprehension of quantum phenomena such as strongly coupled charge and lattice dynamics in quantum materials. By uncovering the tuning knobs available in synthetic crystals, these findings pave the way for further exploration and utilization of electron-phonon coupling in a wide range of scientific and technological applications.
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