Dramatic change of photoexcited quasiparticle relaxation dynamics across Yb valence state transition in YbInCu$_4$

TL;DR

This study reveals how photoexcited quasiparticle relaxation dynamics in YbInCu$_4$ dramatically change across its valence state transition at 40 K, highlighting the temperature-dependent nature of heavy fermion behavior and hybridization effects.

Contribution

It demonstrates the temperature-dependent quasiparticle relaxation dynamics in YbInCu$_4$, linking them to valence state changes and hybridization effects across the phase transition.

Findings

Heavy fermion properties exist only above the transition temperature.

Below the transition, the material behaves like a normal metal despite a hybridization gap.

Fermi level shifts explain the suppression of heavy fermion behavior below T_v.

Abstract

YbInCu$_4$ undergoes a first order structural phase transition near $T_v$=40 K associated with an abrupt change of Yb valence state. We perform ultrafast pump-probe measurement on YbInCu$_4$ and find that the expected heavy fermion properties arising from the \emph{c-f} hybridization exist only in a limited temperature range above $T_v$. Below $T_v$, the compound behaves like a normal metal though a prominent hybridization energy gap is still present in infrared measurement. We elaborate that those seemingly controversial phenomena could be well explained by assuming that the Fermi level suddenly shifts up and becomes far away from the flat \emph{f}-electron band as well as the indirect hybridization energy gap in the mixed valence state below $T_v$.