Coherent energy scale revealed by ultrafast dynamics of UX$_{3}$ (X=Al, Sn, Ga) single crystals

TL;DR

This study uses ultrafast pump-probe spectroscopy to investigate the relaxation dynamics of UX₃ (X=Al, Ga, Sn) single crystals, revealing a coherent energy scale linked to Kondo hybridization and spin density wave formation.

Contribution

It demonstrates that ultrafast optical spectroscopy can detect c-f Kondo hybridization and spin density wave gaps in UX₃ compounds, providing new insights into their electronic coherence.

Findings

UGa₃ shows a spin density wave gap near T_N.

UAl₃ and USn₃ exhibit coherence formation of 5f electrons below T_sf.

Relaxation dynamics fit by Rothwarf-Taylor model confirms sensitivity to Kondo hybridization.

Abstract

Temperature dependence of relaxation dynamics of UX$_{3}$ (X = Al, Ga, Sn) compounds is studied using time resolved pump-probe technique in the reflectance geometry. UGa$_{3}$ is an itinerant antiferromagnet, while UAl$_{3}$ and USn$_{3}$ are spin fluctuation systems. For UGa$_{3}$, our data are consistent with the formation of a spin density wave SDW gap as evidenced from the quasidivergence of the relaxation time $\tau$ near the N\'{e}el temperature $T_{N}$. For UAl$_{3}$ and USn$_{3}$, the relaxation dynamics shows a change from single exponential to two exponential behavior below a particular temperature, suggestive of coherence formation of the 5\textit{f} electrons with the conduction band electrons. This particular temperature can be attributed to the spin fluctuation temperature $T_{sf}$, a measure of the strength of Kondo coherence. Our $T_{sf}$ is consistent with other data such as resistivity and susceptibility measurements. The temperature dependence of the relaxation amplitude and time of UAl$_{3}$ and USn$_{3}$ were also fitted by the Rothwarf-Taylor model. Our results show ultrafast optical spectroscopy is sensitive to c-\textit{f} Kondo hybridization in the \textit{f}-electron systems.