Scientists at the University of California, Irvine, have discovered atomic-scale processes that enhance superconductivity in iron selenide (FeSe), an iron-based material. The findings, published in Nature, could inform future advancements in quantum computing, electronics, and other technologies.
UC Irvine’s Materials Research Institute (IMRI) researchers imaged atomic vibrations using advanced spectroscopy instruments. They identified new phonons — quasiparticles that carry thermal energy — at the interface of an ultrathin FeSe film layered on a strontium titanate (STO) substrate.
“Primarily emerging from the out-of-plane vibrations of oxygen atoms at the interface and in apical oxygens in STO, these phonons couple with electrons due to the spatial overlap of electron and phonon wave functions at the interface,” said lead author Xiaoqing Pan, UC Irvine Distinguished Professor of materials science and engineering, Henry Samueli Endowed Chair in Engineering and IMRI director. “This strong electron-phonon coupling provides a mechanism for enhancing superconductivity transition temperature in ultrathin FeSe.”
The research identified a superconducting transition temperature of 65 K (approximately -340° F) for FeSe, the highest in its class of superconductors. The team also observed that greater uniformity in the FeSe/STO interface correlates with higher transition temperatures, emphasizing the importance of electron-phonon coupling in determining superconducting properties.
“Our vibrational spectroscopy approach enabled us to achieve highly detailed imaging of the vibrations at the superconducting material’s interface with its substrate,” said Pan, who also holds a joint appointment in UC Irvine’s Department of Physics & Astronomy. “The observed variation in interlayer spacing correlates with the superconducting gap, demonstrating the crucial role of spacing in electron-phonon coupling strength and superconductivity.”
“The ultrahigh spatial and energy resolutions of IMRI’s state-of-the-art instruments provided exceptional experimental data for theoretical analysis. The collaboration between simulations and experimental observations enabled precise identification of individual atomic contributions to superconductivity, deepening our understanding of these mechanisms at heterogeneous interfaces,” added co-author Ruqian Wu, UC Irvine Distinguished Professor of Physics and Astronomy.
Pan highlighted the broader implications of the findings for scalable superconductors in applications such as quantum computing, magnetic levitation for mass transportation, and advanced medical diagnostics and treatments.
The study involved collaboration with researchers from Uppsala University in Sweden, Princeton University, Beijing National Laboratory for Condensed Matter Physics, and the Institute of Physics at the Chinese Academy of Sciences. It was funded by the U.S. Department of Energy’s Office of Basic Energy Sciences, Division of Materials Sciences and Engineering.
For more information, visit UC Irvine’s website.
