Surface superconducting state of heavy-fermion superconductor CeIrIn₅ probed by CeIrIn₅-Ag junctions

The CeIrIn₅-Ag junctions of about 2 × 10^-9 cm^-2 area have been made using microfabrication techniques, and the surface superconducting state of CeIrIn₅, which has two characteristic temperatures T₀ and T_c, has been investigated, where T₀ and T_c are the transition temperature to zero-resistivity state and the bulk, thermodynamic transition temperature, respectively. The temperature, below which superconducting anomalies are observed, varies from junction to junction, and yet it is always well above T_c=0.4 K. This result, together with no indication of transition at T_c, suggests that at least the surface of CeIrIn₅ is in the superconducting state above T_c. The data on the critical current I_c in superconducting anomalies point to the possibility to define a local transition temperature for each junction.