Department of Physics and Astronomy , Seoul National University (SNU) , Seoul 08826 , Republic of Korea.
Center for Correlated Electron Systems , Institute for Basic Science (IBS) , Seoul 08826 , Republic of Korea.
Nano Lett. 2019 Feb 13;19(2):1112-1117. doi: 10.1021/acs.nanolett.8b04415. Epub 2019 Jan 30.
In pursuit of the elusive mechanism of high- T superconductors (HTSC), spectroscopic imaging scanning tunneling microscopy (SI-STM) is an indispensable tool for surveying local properties of HTSC. Since a conventional STM utilizes metal tips, which allow the examination of only quasiparticles and not superconducting (SC) pairs, Josephson tunneling using STM has been demonstrated by many authors in the past. An atomically resolved scanning Josephson tunneling microscopy (SJTM), however, was realized only recently on BiSrCaCuO (Bi-2212) below 50 mK and on the Pb(110) surface at 20 mK. Here we report the atomically resolved SJTM on BiSrCaCuO at 4.2 K using Bi-2212 tips created in situ. The I- V characteristics show clear zero bias conductance peaks following Ambegaokar-Baratoff (AB) theory. A gap map was produced for the first time using an atomically resolved Josephson critical current map I ( r) and AB theory. Surprisingly, we found that this new gap map is anticorrelated to the gap map produced by a conventional method relying on the coherence peaks. Quasiparticle resonance due to a single isolated zinc atom impurity was also observed by SJTM, indicating that atomically resolved SJTM was achieved at 4.2 K. Our result provides a starting point for realizing SJTM at even higher temperatures, rendering possible investigation of the existence of SC pairs in HTSC above the T .
为了探索高温超导（HTSC）的 elusive 机制，光谱成像扫描隧道显微镜（SI-STM）是调查 HTSC 局部性质的不可或缺的工具。由于传统的 STM 利用金属尖端，只能检查准粒子而不能检查超导（SC）对，因此过去许多作者已经证明了使用 STM 的约瑟夫森隧道效应。然而，只有最近才在 50 mK 以下的 BiSrCaCuO（Bi-2212）和 20 mK 下的 Pb（110）表面上实现了原子分辨的扫描约瑟夫森隧道显微镜（SJTM）。在这里，我们报告了使用原位创建的 Bi-2212 尖端在 4.2 K 下进行的原子分辨 SJTM。I-V 特性显示出符合 Ambegaokar-Baratoff（AB）理论的清晰零偏置电导峰。首次使用原子分辨约瑟夫森临界电流图 I（r）和 AB 理论生成了间隙图。令人惊讶的是，我们发现这个新的间隙图与依赖于相干峰的常规方法产生的间隙图呈反相关。通过 SJTM 还观察到单个孤立锌原子杂质引起的准粒子共振，表明在 4.2 K 下实现了原子分辨 SJTM。我们的结果为在更高温度下实现 SJTM 提供了起点，有可能在 HTSC 中研究 SC 对的存在。
