Ko Wonhee, Lado Jose L, Maksymovych Petro
Center for Nanophase Materials Sciences, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831, United States.
Department of Applied Physics, Aalto University, 02150 Espoo, Finland.
Nano Lett. 2022 May 25;22(10):4042-4048. doi: 10.1021/acs.nanolett.2c00697. Epub 2022 May 13.
Direct detection of superconductivity has long been a key strength of point-contact Andreev reflection. However, its applicability to atomic-scale imaging is limited by the mechanical contact of the Andreev probe. To this end, we present a new method to probe Andreev reflection in a tunnel junction, leveraging tunneling spectroscopy and junction tunability to achieve quantitative detection of Andreev scattering. This method enables unambiguous assignment of superconducting origins of current-carrying excitations, as well as detection of higher order Andreev processes in atomic-scale junctions. We furthermore revealed distinct sensitivity of Andreev reflection to natural defects, such as step edges, even in classical superconductors. The methodology opens a new path to nano- and atomic-scale imaging of superconducting properties, including disordered superconductors and proximity to phase transitions.
长期以来，直接探测超导性一直是点接触安德烈夫反射的一项关键优势。然而，其在原子尺度成像方面的适用性受到安德烈夫探针机械接触的限制。为此，我们提出了一种在隧道结中探测安德烈夫反射的新方法，利用隧道谱学和结的可调性来实现对安德烈夫散射的定量检测。该方法能够明确确定载流激发的超导起源，还能检测原子尺度结中的高阶安德烈夫过程。我们还发现，即使在经典超导体中，安德烈夫反射对诸如台阶边缘等自然缺陷也具有明显的敏感性。该方法为超导特性的纳米和原子尺度成像开辟了一条新途径，包括无序超导体以及接近相变的情况。
