Second-Harmonic Current-Phase Relation in Josephson Junctions with Ferromagnetic Barriers

M. J. A. Stoutimore, A. N. Rossolenko, V. V. Bolginov, V. A. Oboznov, A. Y. Rusanov, D. S. Baranov, N. Pugach, S. M. Frolov, V. V. Ryazanov, and D. J. Van Harlingen

Phys. Rev. Lett. 121, 177702 – Published 26 October 2018

Abstract

We report the observation of a current-phase relation dominated by the second Josephson harmonic in superconductor-ferromagnet-superconductor junctions. The exotic current-phase relation is realized in the vicinity of a temperature-controlled 0-to- $π$ junction transition, at which the first Josephson harmonic vanishes. Direct current-phase relation measurements, as well as Josephson interferometry, nonvanishing supercurrent and half-integer Shapiro steps at the $0 − π$ transition self-consistently point to an intrinsic second harmonic term, making it possible to rule out common alternative origins of half-periodic behavior. While surprising for diffusive multimode junctions, the large second harmonic is in agreement with theory predictions for thin ferromagnetic interlayers.

Received 7 June 2018

DOI:https://doi.org/10.1103/PhysRevLett.121.177702

Physics Subject Headings (PhySH)

FFLO Josephson effect Proximity effect Superconducting RF

Junctions Low-temperature superconductors Multilayer thin films SQUID Superconducting devices

Condensed Matter, Materials & Applied Physics

Authors & Affiliations

M. J. A. Stoutimore¹, A. N. Rossolenko², V. V. Bolginov^2,3,4, V. A. Oboznov², A. Y. Rusanov², D. S. Baranov^2,5, N. Pugach^3,6, S. M. Frolov⁷, V. V. Ryazanov^2,4,8, and D. J. Van Harlingen¹

¹Department of Physics, University of Illinois at Urbana-Champaign, Urbana, Illinois 61801, USA
²Institute of Solid State Physics, Russian Academy of Sciences, Chernogolovka 142432, Russia
³Skobeltsyn Institute of Nuclear Physics, Lomonosov Moscow State University, Moscow 119991, Russia
⁴Russian National University of Science and Technology (NUST) MISiS, 4 Leninsky Prospect, Moscow 119049, Russia
⁵Moscow Institute of Physics and Technology, Dolgoprudny 141700, Russia
⁶MIEM, National Research University Higher School of Economics, Moscow 101000, Russia
⁷Department of Physics and Astronomy, University of Pittsburgh, Pittsburgh, Pennsylvania 15260, USA
⁸Faculty of Physics, National Research University Higher School of Economics, Moscow 101000, Russia