Ir 5d-band derived superconductivity in LaIr₃

The superconducting properties of rhombohedral LaIr₃ were examined using susceptibility, resistivity, heat capacity, and zero-field (ZF) and transverse-field (TF) muon spin relaxation and rotation (μSR) measurements. The susceptibility and resistivity measurements confirm a superconducting transition below T_c K. Two successive transitions are observed in the heat capacity data, one at T_c K and a second at 1.2 K below T_c. The heat capacity jump is ΔC/γT_c 10, which is lower than 1.43 expected for Bardeen-Cooper-Schrieffer (BCS) weak-coupling limit. TF-μSR measurements reveal a fully gapped s-wave superconductivity with 2Δ(0)/kbT_c=3.31(8), which is small compared to the BCS value of 3.56, suggesting weak-coupling superconductivity. The magnetic penetration depth, λl(0), estimated from TF-μSR gives λL(0)=386(3) nm, a superconducting carrier density ns=2.9(1)×10²⁷ carriers m^-3 and a carrier effective-mass enhancement factor m*=1.53(1)me. ZF-μSR data show no evidence for any spontaneous magnetic fields below T_c, which demonstrates that time-reversal symmetry is preserved in the superconducting state of LaIr₃.