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, researchers 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.
They measured the electrical current between an atomically sharp metallic tip and a superconductor and how the current depended on the separation between the tip and the superconductor. This enabled them to detect the amount of Andreev reflection going back to the superconductor, while maintaining an imaging resolution comparable to individual atoms. The experimental results corresponded exactly to Lado’s theoretical model.
This experimental detection of Cooper pairs at the atomic scale provides an entirely new method for understanding quantum materials.
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. They 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.
SOURCE – ACS Nanoletters
Written by Brian Wang, Nextbigfuture.com
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