Quasiparticle relaxation across the spin-density-wave gap in the itinerant antiferromagnet U Ni Ga 5

Time-resolved photoinduced reflectivity is measured for the itinerant antiferromagnet $\mathrm{U}\mathrm{Ni}{\mathrm{Ga}}_{5}$ $({T}_{N}\ensuremath{\approx}85\phantom{\rule{0.3em}{0ex}}\mathrm{K})$ from room temperature to $10\phantom{\rule{0.3em}{0ex}}\mathrm{K}$. The relaxation time $\ensuremath{\tau}$ shows a sharp increase at ${T}_{N}$ consistent with the opening of a spin-density-wave (SDW) gap. The temperature dependence of $\ensuremath{\tau}$ below ${T}_{N}$ 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 $\mathrm{Ce}\mathrm{Co}{\mathrm{In}}_{5}$ where the recombination bottleneck arises from the hybridization gap.