Quasiparticle Relaxation Across a Spin Gap in the Itinerant Antiferromagnet UNiGa5

TL;DR

This study uses ultrafast spectroscopy to investigate quasiparticle relaxation in UNiGa5, revealing a spin gap opening at the Néel temperature that affects quasiparticle dynamics, distinct from heavy fermion behavior.

Contribution

It provides the first detailed ultrafast measurement of quasiparticle relaxation across a spin gap in an itinerant antiferromagnet, highlighting differences from heavy fermion systems.

Findings

Relaxation time sharply increases at the Néel temperature.

Temperature dependence below T_N is consistent with a spin gap opening.

Recombination bottleneck is explained by the Rothwarf-Taylor model.

Abstract

Ultrafast time-resolved photoinduced reflectivity is measured for the itinerant antiferromagnet UNiGa$_{5}$ ($T_{N} \approx$85 K) from room temperature to 10 K. The relaxation time $\tau$ shows a sharp increase at $T_{N}$ consistent with the opening of a spin gap. In addition, the temperature dependence of $\tau$ below $T_{N}$ is consistent with the opening of a spin gap leading to a quasiparticle recombination bottleneck as revealed by the Rothwarf-Taylor model. This contrasts with canonical heavy fermions such as CeCoIn$_{5}$ where the recombination bottleneck arises from the hybridization gap.