Probing the current-phase relation in Josephson point-contact junctions between [Formula: see text] In[Formula: see text] and [Formula: see text] K[Formula: see text] (FeAs)[Formula: see text] superconductors

The Josephson effect in point contacts between an “ordinary” superconductor [Formula: see text] In[Formula: see text] ([Formula: see text] ) and single crystals of the Fe-based superconductor Ba[Formula: see text] K[Formula: see text] (FeAs)[Formula: see text] ([Formula: see text] ), was investigated. In order to shed light on the order parameter symmetry of Ba[Formula: see text] K[Formula: see text] (FeAs)[Formula: see text] , the dependence of the Josephson supercurrent [Formula: see text] on the temperature and on [Formula: see text] with [Formula: see text] was studied. The dependencies of the critical current on temperature [Formula: see text] and of the amplitudes of the first current steps of the current–voltage characteristic [Formula: see text] [Formula: see text] on the power of microwave radiation with frequency [Formula: see text] were measured. It is shown that the dependencies [Formula: see text] are close to the well-known Ambegaokar–Baratoff (AB) dependence for tunnel contacts between “ordinary” superconductors and to the dependence calculated by Burmistrova et al. (Phys Rev B 91, 214501 (2015)) for microshorts between an “ordinary” superconductor and a two-band superconductor with [Formula: see text] order parameter symmetry at certain values of the transparency of boundaries and thickness of the transition layer. It is found that the dependencies [Formula: see text] cannot be approximated within the resistively shunted model using the normalized microwave frequencies [Formula: see text] with characteristic voltages [Formula: see text] , [Formula: see text] —normal resistance of the contact) found from the low-voltage parts of the current–voltage characteristics. The reasons for this failure are discussed and a method is proposed for accurately determining the value of [Formula: see text] , which takes into account all the features of the point contact affecting the period of the dependence [Formula: see text] . An analysis of the [Formula: see text] and [Formula: see text] dependencies shows that the superconducting current of the Josephson contacts under investigation is proportional to the [Formula: see text] of the phase difference [Formula: see text] , [Formula: see text] . The implications of these results on the symmetry of the order parameter are also discussed.