Abstract
Characteristics of the Josephson effect in Pb0.6In0.4/FeSe0.4Te0.6 point contacts with the current flowing parallel to ab plane of the iron chalcogenide crystal (with critical temperature Tc ≈ 15 K) have been studied. Dependences of the critical current Ic and amplitudes In of the first steps of current (Shapiro steps) in the current–voltage (I–V) characteristics (n = 0, 1, 2; I0 = Ic) on the microwave power P (at frequency f = 7.6 GHz) and dependences of the characteristic voltage Vc(T) = IcRN (RN being the normal state resistance) on the temperature T have been measured. It is found that the characteristics of contacts (Ic, RN, Vc) obtained for initial parts of the I–V curves do not adequately describe the oscillations of current steps in the microwave radiation field. A method is proposed for determining the normalized microwave frequency Ω = 2πf(2eVc/\(\hbar \))–1 that provides quantitative description of the current oscillation steps in the framework of a resistive contact model and allows one to check that the Josephson superconducting current Is is proportional to sin(aφ) (a = 1, 2), where φ is the phase difference of the order parameters. Comparison of the measured In(\(\sqrt P \)) curves to those calculated using the resistive model showed that Is = Icsinφ, in agreement with the conventional s and s++ symmetry of the order parameter in FeSe0.4Te0.6. It is established that Vc of the contacts studied is proportional to T in a wide temperature interval.
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ACKNOWLEDGMENTS
The authors are grateful to laboratory colleagues for kindly providing FeSe0.4Te0.6 crystal sample and to S.I. Vedeneev for fruitful discussions.
Funding
The study was supported in part by the Program of Fundamental Investigations of the Presidium of the Russian Academy of Sciences in the part of “Topical Problems of Low-Temperature Physics.”
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Translated by P. Pozdeev
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Stepanov, V.A., Golubkov, M.V. The Josephson Effect in PbIn/Fe1 –ySe1 –xTex Point Contacts: Probing the Order Parameter Symmetry. J. Exp. Theor. Phys. 130, 204–213 (2020). https://doi.org/10.1134/S1063776120020156
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DOI: https://doi.org/10.1134/S1063776120020156