On the origin of the zero-resistance anomaly in heavy fermion superconducting Ir: a clue from magnetic field and Rh-doping studies

We present the results of the specific heat and AC magnetic susceptibility measurements of $CeIr_{1-x}Rh_xIn_5$ for x from 0 to 0.5. As x is increased from 0 both quantities reflect the competition between two effects. The first is a suppression of superconductivity below the bulk transition temperature of T$_c = 0.4$ K, which is due to the pair breaking effect of Rh impurities. The second is an increase in the volume fraction of the superconducting regions above T$_c$, which we attribute to defect-induced strain. Analysis of the H-T phase diagram for CeIrIn$_5$obtained from the bulk probes and resistance measurements points to the filamentary origin of the inhomogeneous superconductivity at T$_\rho \approx 1.2$ K, where the resistance drops to zero. The identical anisotropies in the magnetic field dependence of the specific heat and the resistance anomalies in CeIrIn$_5$ indicate that the filamentary superconductivity is intrinsic, involving electrons from the part of the Fermi surface responsible for bulk superconductivity.