Fan Jia-Qi, Yu Xue-Qing, Cheng Fang-Jun, Wang Heng, Wang Ruifeng, Ma Xiaobing, Hu Xiao-Peng, Zhang Ding, Ma Xu-Cun, Xue Qi-Kun, Song Can-Li
State Key Laboratory of Low-Dimensional Quantum Physics, Department of Physics, Tsinghua University, Beijing 100084, China.
Natl Sci Rev. 2021 Dec 15;9(4):nwab225. doi: 10.1093/nsr/nwab225. eCollection 2022 Apr.
The microscopic understanding of high-temperature superconductivity in cuprates has been hindered by the apparent complexity of crystal structures in these materials. We used scanning tunneling microscopy and spectroscopy to study the electron-doped copper oxide compound Sr Nd CuO, which has only bare cations separating the CuO planes and thus the simplest infinite-layer structure of all cuprate superconductors. Tunneling conductance spectra of the major CuO planes in the superconducting state revealed direct evidence for a nodeless pairing gap, regardless of variation of its magnitude with the local doping of trivalent neodymium. Furthermore, three distinct bosonic modes are observed as multiple peak-dip-hump features outside the superconducting gaps and their respective energies depend little on the spatially varying gaps. As well as the bosonic modes, with energies identical to those of the external, bending and stretching phonons of copper oxides, our findings reveal the origin of the bosonic modes in lattice vibrations rather than spin excitations.
这些材料中晶体结构的明显复杂性阻碍了对铜酸盐高温超导性的微观理解。我们使用扫描隧道显微镜和光谱学研究了电子掺杂的氧化铜化合物Sr Nd CuO，该化合物中只有裸阳离子分隔CuO平面，因此是所有铜酸盐超导体中最简单的无限层结构。超导状态下主要CuO平面的隧道电导谱揭示了无节点配对能隙的直接证据，而与三价钕的局部掺杂引起的能隙大小变化无关。此外，在超导能隙之外观察到三种不同的玻色子模式，表现为多个峰-谷-峰特征，它们各自的能量几乎不依赖于空间变化的能隙。除了能量与氧化铜的外部、弯曲和拉伸声子相同的玻色子模式外，我们的研究结果还揭示了玻色子模式起源于晶格振动而非自旋激发。
