In single unit-cell FeSe grown on SrTiO₃, the superconductivity transition temperature features a significant enhancement. Local phonon modes at the interface associated with electron-phonon coupling may play an important role in the interface-induced enhancement. However, such phonon modes have eluded direct experimental observations. The complicated atomic structure of the interface brings challenges to obtain the accurate structure-phonon relation knowledge. Here, we achieve direct characterizations of atomic structure and phonon modes at the FeSe/SrTiO₃ interface with atomically resolved imaging and electron energy loss spectroscopy in an electron microscope. We find several phonon modes highly localized (~1.3 nm) at the unique double layer Ti-O terminated interface, one of which (~ 83 meV) engages in strong interactions with the electrons in FeSe based on ab initio calculations. This finding of the localized interfacial phonon associated with strong electron-phonon coupling provides new insights into understanding the origin of superconductivity enhancement at the FeSe/SrTiO₃ interface.

在SrTiO ₃上生长的单晶胞FeSe中，超导转变温度显着提高。与电子声子耦合相关的界面处的局域声子模式可能在界面诱导增强中发挥重要作用。然而，这种声子模式无法直接进行实验观察。界面复杂的原子结构给获得准确的结构-声子关系知识带来了挑战。在这里，我们通过电子显微镜中的原子分辨成像和电子能量损失光谱，实现了 FeSe/SrTiO ₃界面处原子结构和声子模式的直接表征。我们在独特的双层 Ti-O 端接界面上发现了几种高度局域化的声子模式（约 1.3 nm），其中一种声子模式（约 83 meV）基于从头算计算，与 FeSe 中的电子发生强烈相互作用。与强电子声子耦合相关的局域界面声子的发现为理解 FeSe/SrTiO ₃界面超导增强的起源提供了新的见解。