Construction of tunnel junction and research on Josephson effect in iron-based superconductors

As one of the most significant physical characteristics of superconductors, the Josephson effect serves as the foundation of superconducting electronics applications and holds considerable value in fundamental research. In this work, we carried out investigations on the Josephson effect in two systems of iron -based superconductors: KCa2Fe4As4F2 and FeSe0.5Te0.5. We studied the intrinsic Josephson effect in KCa2Fe4As4F2 single crystals based on the structural characteristics of alternating stacking of conductive and insulating layers and the resultant strong anisotropy. With micro/ nano -fabrication, the sample size and critical current are successfully reduced, considerably decreasing the influence of the thermal effect on the measurements. Finally, information regarding the superconducting energy gap is obtained by fitting the temperature -dependent critical current behavior using the A -B equation based on superconducting electron tunneling. The behavior of superconducting quantum diffraction in terms of the periodic oscillation of critical current with the in -plane magnetic field is observed, confirming the existence of the intrinsic Josephson effect in this 12442 system. Additionally, a Josephson tunnel junction was prepared in ultrathin FeSe0.5Te0.5 single crystals by mechanical exfoliation, and the evolution behavior of its critical current with temperature and magnetic field was obtained. The analysis shows that the A -B equation can accurately describe the temperature dependence of the critical current. Furthermore, the extracted superconducting energy gap value from the fitting is consistent with previous reports.