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 Tc, has been investigated, where T0 and Tc 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 Tc=0.4 K. This result, together with no indication of transition at Tc, suggests that at least the surface of CeIrIn5 is in the superconducting state above Tc. The data on the critical current Ic in superconducting anomalies point to the possibility to define a local transition temperature for each junction.