| Recently, the discovery of iron-based superconductor (SC) has attracted much attention. For the newly discovered high-temperature SC with unconventional behaviors, one of important issues which it is confronted with, is the determination of the pair potential symmetry. Experimentally, one can study Josephson junctions to obtain the information of the pairing mechanisms and gap energy.In this article, using an extended Blonder-Tinham_Klapwijk (BTK) approach, we theoretically study relevant Josephson junctions composed of iron-based SCs and obtain the variations of critical Josephson current Ic with interband coupling strength, ferromagnet (FM) width, spin polarization, and interface barrier strength, and then the dependence of the current Ⅰ on the phase, at the same time, compare the results with those for the corresponding s++-wave model and provide theoretical guidance for experimentally probing and confirming the pairing symmetry of the iron-based SC. The Josephson junctions consisting of iron-based SCs are mainly studied from four aspects in the article.Firstly, we study the s-wave SC/normal metal/s±-wave SC Josephson junction. A0～π transition as a function of interband coupling strength a is shown to be always exhibited and can be experimentally used to discriminate the pairing symmetry in the iron-based SCs from the s++-wave one in MgB2. The mechanism is extrinsic, the tuning of mixing between the two trajectories with opposite phases and consequent twofold Andreev reflections, differing from that as a function of FM width in s-wave SC/FM/s-wave SC junction, the inner nature of the trajectory with different spin, i.e., intrinsic.Secondly, the s±-wave SC/normal metal/s±-wave SC Josephson junction is investigated. It is found that the features are the same as those in the Josephson junction of the first case, however, there exist some slight differences, for instance, regardless of the interfacial barrier strength, the interband coupling strength becomes small for all corresponding dips.Thirdly, we study the s±-wave SC/FM/s±-wave SC Josephson junction. It is shown that the features of damped oscillations of critical Josephson current Ic as a function of FM width, the split of peaks resulted in by the interband coupling in the s±-wave SC, is much distinct from that for s++-wave SC/FM/s++-wave SC junctions. In particular, a0～π transition as a function of a is always found to exhibit with the corresponding dip shifting toward to the large a due to enhancing the spin polarization in the FM, while there exists no0～π transition for the SC with s++-wave pairing symmetry. Likewise, the two features can be experimentally used to distinguish the pairing symmetry in the iron-based SC and the s++-wave one in MgB2.Lastly, the s±-wave SC junctions with a spacer of strong FM are studied. It is shown that, the damped oscillations of critical Josephson current Ic as a function of interband coupling strength have many dips, corresponding to the transitions of0～π or π～0junction., which can be also used for experimentally probing and identifying the s±-wave pairing symmetry in the iron-based SCs different from the s++-wave one in MgB2.Moreover, by tuning the doping level in the s±-wave SCs, one can vary the interband coupling strength so as to obtain the controllable0～π transition. These devices may be realized with current technologies and have practical use in Cooper pair spintronics and quantum information. |
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