Abstract
We investigated the Josephson effect between the conventional superconductor Pb0.7In0.3 and Ba0.4K0.6 (FeAs)2 single crystals by performing directional point-contact experiments. The junctions were irradiated with microwaves and the behavior of the Shapiro steps as a function of the square root of the microwave power was studied by means of the RSJ model extended to the nonautonomous case with an rf current-source term. The analysis reveals that, for current injection along the ab plane, the current-phase relation deviates from being simply described by the standard sin(ϕ) (as we indeed observed along the c axis) and a dominant sin(2ϕ) component is observed. The results are compared with a theory of the dc Josephson effect, formulated by using a method based on the calculation of temperature Green’s function in the junction within the tight-binding model (Burmistrova et al., Phys. Rev. B 91, 214501, 2015). The comparison shows that the experimental results here presented strongly favor an s ±-wave symmetry of the order parameter in this compound.
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Acknowledgments
We gratefully acknowledge D. J. Van Harlingen, and P. Seidel for their valuable discussions. We thank W. K. Park, J. M. Atkinson Mora, R. W. Giannetta, and J. Ku for their technical support. V.A.S. acknowledges the Russian Academy of Sciences Division of Physical Sciences (program 3, code 203). R.S.G. acknowledges the support by the European Community through the Collaborative EU-Japan Project IRON SEA (NMP3-SL-2011283141) and by the Italian Ministry of University and Research (MIUR) through the PRIN 2012 Project RIDEIRON (2012X3YFZ2 005).M.T. acknowledges the U.S.-Italy Fulbright Commission, Core Fulbright Visiting Scholar Program, during which the experimental results presented here were collected. At UIUC, the research of M.T. and L.H.G. are primarily supported by the Center for Emergent Superconductivity, Department of Energy Frontier Research Center under Grant No. DEAC0298CH1088. L.H.G. also received some support from the National Science Foundation Division of Materials Research (DMR) Award No. 12-06766.
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Tortello, M., Stepanov, V.A., Ding, X. et al. Directional Point-Contact Josephson Junctions on Ba0.4K0.6(FeAs)2 Single Crystals. J Supercond Nov Magn 29, 679–683 (2016). https://doi.org/10.1007/s10948-015-3323-z
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DOI: https://doi.org/10.1007/s10948-015-3323-z