Thermal Fluctuations in Pb–Ag–Pb (SNS) Josephson Junctions in Magnetic Fields

Abstract

A systematic investigation of the thermal fluctuation effects has been carried out on Pb–Ag–Pb (superconductor-normal metal-superconductor) Josephson junctions with special emphasis on the critical current I_c(H) in magnetic fields. Thick normal-metal barriers (∼15000 Å) are prepared in order to suppress the Josephson coupling energy between the two superconductors. Thermal fluctuations can significantly break the superconducting phase coupling and then lead to a decrease of the oscillation amplitude of I_c(H). In the presence of strong fluctuations, the envelope of the maxima in the Fraunhofer diffraction pattern is proportional to 1⁄H² and not to 1⁄H as in the absence of thermal fluctuations. The experimental results are in agreement with theoretical predictions of Ivanchenko and Zil’berman.