Transparency-controlled multiple charge transfer in superconducting junctions with local shot-noise scanning tunneling spectroscopy

arXiv (Cornell University)

Abstract

Charge transport in superconducting junctions at finite voltages is governed by Andreev reflections, including multiple Andreev reflections, which are processes that enable multiple charge transfer, a hallmark that shot noise can directly quantify. Since the effective charge extracted from shot noise measurements varies with the transparency of the junction, systematic control of transparency is essential but experimentally challenging. Here, we present shot noise scanning tunneling microscopy measurements enabled by a newly developed amplifier, allowing access to different transparency regimes. We perform shot noise measurements on Pb(111) with tunable transparency at 2.2 K and observe that the shot noise evolves from a single electron tunneling regime to multiple charge transfer regime as transparency increases. Our results are quantitatively consistent with theoretical simulations of Andreev reflections and multiple Andreev reflections for a single-channel system. These results establish junction transparency as the key parameter governing the evolution of charge transport and demonstrate that noise-STM is a powerful platform for investigating microscopic charge transport mechanisms with controlled junction transparency at the atomic scale.

Authors 9

1. Yudai Sato
2. Maialen Ortego Larrazabal Aachen

   Leiden University · Utrecht University

   Affiliation as printed

   Debye Institute of Nanomaterials Science , Utrecht University , PO Box 80000 , 3508 TA Utrecht , The Netherlands

   Leiden Institute of Physics , Leiden University , Niels Bohrweg 2 , 2333 CA Leiden , The Netherlands

3. Jian-Feng Ge Aachen

   Leiden University · Max Planck Institute for Chemical Physics of Solids

   Affiliation as printed

   Leiden Institute of Physics , Leiden University , Niels Bohrweg 2 , 2333 CA Leiden , The Netherlands

   Max Planck Institute for Chemical Physics of Solids , 01187 Dresden , Germany

4. Ingmar Swart

   Utrecht University

   Affiliation as printed

   Debye Institute of Nanomaterials Science , Utrecht University , PO Box 80000 , 3508 TA Utrecht , The Netherlands

5. Doohee Cho

   Yonsei University

   Affiliation as printed

   Department of Physics , Yonsei University , Seoul 03722 , Republic of Korea

6. Wolfgang Belzig

   University of Konstanz

   Affiliation as printed

   Fachbereich Physik , Universität Konstanz , 78457 Konstanz , Germany

7. Juan Carlos Cuevas

   Universidad Autónoma de Madrid

   Affiliation as printed

   Condensed Matter Physics Center (IFIMAC) , Universidad Autónoma de Madrid , E-28049 Madrid , Spain

   Departamento de Física Teórica de la Materia Condensada , Universidad Autónoma de Madrid , E-28049 Madrid , Spain

8. Milan P. Allan
9. Jiasen Niu