Zhang Xiaowen, Xu Tiequan, Shi Ruochen, Han Bo, Liu Fachen, Liu Zhetong, Gao Xiaoyue, Du Jinlong, Wang Yue, Gao Peng
International Center for Quantum Materials, School of Physics, Peking University, Beijing 100871, China.
Electron Microscopy Laboratory, School of Physics, Peking University, Beijing 100871, China.
Nano Lett. 2024 Oct 23;24(42):13200-13205. doi: 10.1021/acs.nanolett.4c03170. Epub 2024 Oct 8.
In conventional Bardeen-Cooper-Schrieffer (BCS) superconductors, electron-phonon coupling is the fundamental mechanism of superconductivity. For instance, the superconductivity of magnesium diboride (MgB) comes from the coupling between modes (in-plane boron-boron bond vibrations) and self-doped charge carriers. In thin films and ceramics of BCS superconductors, interfaces with discontinuous chemical bonds may alter the local electron-phonon coupling. However, such effects remain largely unexplored. Here, we investigate the heterointerface of the MgB film on the SiC substrate at the atomic scale using electron microscopy and spectroscopy. We detect the presence of a thin MgO layer with a thickness of ∼1 nm between MgB and SiC. Atomic-level electron energy loss spectra (EELS) show MgB- mode splitting and softening near the MgB/MgO interface, which enhances electron-phonon coupling at the interface. Our findings highlight the potential of interface engineering to enhance superconductivity via modulating local phonon states and/or electron states.
在传统的巴丁-库珀-施里弗（BCS）超导体中，电子-声子耦合是超导性的基本机制。例如，二硼化镁（MgB₂）的超导性来自于σ模式（面内硼-硼键振动）与自掺杂电荷载流子之间的耦合。在BCS超导体的薄膜和陶瓷中，具有不连续化学键的界面可能会改变局部电子-声子耦合。然而，此类效应在很大程度上仍未得到探索。在此，我们使用电子显微镜和光谱学在原子尺度上研究了SiC衬底上MgB₂薄膜的异质界面。我们检测到在MgB₂和SiC之间存在一层厚度约为1 nm的薄MgO层。原子级电子能量损失谱（EELS）显示在MgB₂/MgO界面附近MgB₂的σ模式分裂和软化，这增强了界面处的电子-声子耦合。我们的研究结果突出了通过调节局部声子态和/或电子态来增强超导性的界面工程潜力。
