Ultrafast quasiparticle relaxation dynamics in normal metals and heavy fermion materials

TL;DR

This paper provides a theoretical analysis of ultrafast quasiparticle relaxation in normal metals and heavy fermion materials, revealing distinct temperature-dependent behaviors and proposing mechanisms for electron-phonon scattering dynamics.

Contribution

It introduces a comprehensive theoretical framework explaining quasiparticle relaxation times and blocking mechanisms in heavy fermion systems, differing from previous models.

Findings

Normal metals show temperature-independent relaxation times at low T.

Heavy fermion materials exhibit increased relaxation times below the Kondo temperature.

Proposed blocking mechanism due to Fermi velocity differences explains observed dynamics.

Abstract

We present a detailed theoretical study of the ultrafast quasiparticle relaxation dynamics observed in normal metals and heavy fermion materials with femtosecond time-resolved optical pump-probe spectroscopy. For normal metals, a nonthermal electron distribution gives rise to a temperature (T) independent electron-phonon relaxation time at low temperatures, in contrast to the T^{-3}-divergent behavior predicted by the two-temperature model. For heavy fermion compounds, we find that the blocking of electron-phonon scattering for heavy electrons within the density-of-states peak near the Fermi energy is crucial to explain the rapid increase of the electron-phonon relaxation time below the Kondo temperature. We propose the hypothesis that the slower Fermi velocity compared to the sound velocity provides a natural blocking mechanism due to energy and momentum conservation laws.