Evidence of d-wave pairing symmetry of the gap of the heavy-fermion superconductor CeIrIn5 from magnetic-penetration-depth measurements

The heavy-Fermion compounds CeTIn5, where T is Co, Ir, or Rh, exhibit two distinct superconducting regimes upon tuning the lattice density via doping or pressure. CeIrIn5 is close to the boundary and there is some disagreement on whether its superconducting state is the same as CeCoIn5 or not. In this Brief Report, we report the low-temperature penetration-depth lambda(T) measurements for CeIrIn5. That lambda(T)proportional to T below 0.3T(c), irrespective of sample orientation, confirms the existence of line nodes in the gap with no evidence for the point node proposed in a hybrid-gap structure.