The emergent superconductivity at the LaAlO3/KTaO3 interfaces exhibits a mysterious dependence on the KTaO3 crystallographic orientations. Here we show, by soft X-ray angle-resolved photoemission spectroscopy, that the interfacial superconductivity is contributed by mobile electrons with unexpected quasi-three-dimensional character, beyond the "two-dimensional electron gas" scenario in describing oxide interfaces. At differently-oriented interfaces, the quasi-three-dimensional electron gas ubiquitously exists and spatially overlaps with the small q Fuchs-Kliewer surface phonons. Intriguingly, electrons and the Fuchs-Kliewer phonons couple with different strengths depending on the interfacial orientations, and the stronger coupling correlates with the higher superconducting transition temperature. Our results provide a natural explanation for the orientation-dependent superconductivity, and the first evidence that interfacial orientations can affect electron-phonon coupling strength over several nanometers, which may have profound implications for the applications of oxide interfaces in general.
@article{arxiv.2301.13488,
title = {Orientation-dependent electron-phonon coupling in interfacial superconductors LaAlO3/KTaO3},
author = {Xiaoyang Chen and Tianlun Yu and Yuan Liu and Yanqiu Sun and Minyinan Lei and Nan Guo and Yu Fan and Xingtian Sun and Meng Zhang and Fatima Alarab and Vladimir N. Strokov and Yilin Wang and Tao Zhou and Xinyi Liu and Fanjin Lu and Weitao Liu and Yanwu Xie and Rui Peng and Haichao Xu and Donglai Feng},
journal= {arXiv preprint arXiv:2301.13488},
year = {2024}
}