Resonant Andreev reflections probed by photon-assisted tunnelling at the atomic scale
Resonant Andreev reflections probed by photon-assisted tunnelling at the atomic scale
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DOI：
10.1038/s41567-020-0972-z
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发表时间：
2020-07-27
期刊：
影响因子：
19.6
通讯作者：
Franke, Katharina J.
中科院分区：
文献类型：
--
作者：
Peters, Olof;Bogdanoff, Nils;Franke, Katharina J.
扫描隧道显微镜是增强微波辐射，允许光子辅助隧道过程。该技术在超导体杂质态上得到了证明。穿越超导结的隧穿是通过多种多样的过程进行的，这些过程通过多次安德烈夫反射转移单个电子、库珀对甚至更多的电子。光子辅助隧穿与古老的Tien-Gordon模型相结合，长期以来一直是识别超导体之间隧穿过程的有力工具。在这里，我们通过将超导尖端的扫描隧道显微镜暴露在微波辐射下，探测包括杂质诱导的Yu-Shiba-Rusinov （YSR）状态的超导隧道结。我们发现一个简单的Tien-Gordon描述描述了单电子和库珀对隧穿到裸露的衬底中，但在通过YSR态通过共振Andreev反射隧穿时被破坏了。我们开发了一个改进的理论描述，与数据非常吻合。我们的研究结果建立了光子辅助隧穿作为一种强大的工具来分析原子尺度上的隧穿过程，这对于非常规和拓扑超导体来说应该是特别有用的。
Scanning tunnelling microscopy is enhanced by microwave radiation that allows photon-assisted tunnelling processes. This technique is demonstrated on impurity states in a superconductor.Tunnelling across superconducting junctions proceeds by a rich variety of processes, which transfer single electrons, Cooper pairs or even larger numbers of electrons by multiple Andreev reflections. Photon-assisted tunnelling combined with the venerable Tien-Gordon model has long been a powerful tool to identify tunnelling processes between superconductors. Here, we probe superconducting tunnel junctions including an impurity-induced Yu-Shiba-Rusinov (YSR) state by exposing a scanning tunnelling microscope with a superconducting tip to microwave radiation. We find that a simple Tien-Gordon description describes tunnelling of single electrons and Cooper pairs into the bare substrate, but breaks down for tunnelling via YSR states by resonant Andreev reflections. We develop an improved theoretical description that is in excellent agreement with the data. Our results establish photon-assisted tunnelling as a powerful tool to analyse tunnelling processes at the atomic scale, which should be particularly informative for unconventional and topological superconductors.