Anisotropic Superconducting Gap in Transuranium Superconductor PuRhGa5: Ga NQR Study on a Single Crystal

Abstract

69,71 Ga NMR/NQR studies have been performed on a single crystal of the transuranium superconductor PuRhGa 5 with T c ≃9 K. We have observed a 69 Ga NQR line at ∼29.15 MHz, and assigned it to the 4 i Ga site using the NMR results. The 69 Ga NQR spin–lattice relaxation rate 1/ T 1 shows no coherence peak just below T c , but obeys T 3 behavior below T c . This result strongly suggests that PuRhGa 5 is an unconventional superconductor having an anisotropic superconducting gap. The gap amplitude 2Δ 0 ( T →0)≃5 k B T c and the residual density of states N res ( T =0)/ N 0 ( T = T c )≃0.25 have been determined assuming a simple polar function of the form Δ(θ,φ)=Δ 0 cos θ, where θ and φ are angular parameters on the Fermi surface.