Quasiparticle relaxation across the spin-density-wave gap in the itinerant antiferromagnet UNi Ga5

Time-resolved photoinduced reflectivity is measured for the itinerant antiferromagnet UNi Ga5 (TN ≈85 K) from room temperature to 10 K. The relaxation time τ shows a sharp increase at TN consistent with the opening of a spin-density-wave (SDW) gap. The temperature dependence of τ below TN is also consistent with the opening of a SDW gap leading to a quasiparticle recombination bottleneck as revealed by the Rothwarf-Taylor model. This contrasts with canonical heavy fermions such as CeCo In5 where the recombination bottleneck arises from the hybridization gap.