Hot electron relaxation in a heavy fermion system with tuned doping

TL;DR

This study uses femtosecond spectroscopy to explore how doping affects electron relaxation and the hybridization gap in a heavy fermion system, revealing persistent gaps and a doping-dependent relaxation bottleneck.

Contribution

It provides new insights into the doping dependence of hybridization gaps and relaxation dynamics in heavy fermion materials using time-resolved spectroscopy.

Findings

Hybridization gap persists up to 30% doping.

Relaxation time divergence is truncated below a doping-dependent temperature T*(x).

A theoretical model explains the doping and temperature dependence of relaxation dynamics.

Abstract

Femtosecond time-resolved optical spectroscopy was used to systematically study photoexcited carrier relaxation dynamics in the intermediate-valence heavy fermion system Yb1-xLuxAl3 (0 < x < 1). Given the demonstrated sensitivity of this experimental technique to the presence of the low energy gaps in the charge excitation spectrum, the aim of this work was to study the effect of dilution of the Kondo lattice on its low energy electronic structure. The results imply that in Yb1-xLuxAl3 the hybridization gap, resulting from hybridization of local moments and conduction electrons, persists up to 30% doping. Interestingly, below some characteristic, doping dependent temperature T*(x) the relaxation time divergence, governed by the relaxation bottleneck due to the presence of the indirect hybridization gap, is truncated. This observation is attributed to the competing ballistic transport of hot electrons out of the probed volume at low temperatures. The derived theoretical model accounts for both the functional form of relaxation dynamics below T*(x), as well as the doping dependence of the low temperature relaxation rate in Yb1-xLuxAl3.