Intact Quasiparticles at an Unconventional Quantum Critical Point

TL;DR

This study investigates the behavior of quasiparticles near an unconventional quantum critical point in a heavy-fermion metal, revealing the preservation of quasiparticles and unique non-Fermi liquid scattering characteristics at very low temperatures.

Contribution

It provides evidence that Landau quasiparticles remain intact at an unconventional quantum critical point, challenging theories of quasiparticle breakdown in such systems.

Findings

Wiedemann-Franz law obeyed at lowest temperatures

Non-Fermi liquid T-linear inelastic scattering observed

Identification of a new temperature scale around 0.3 K

Abstract

We report measurements of in-plane electrical and thermal transport properties in the limit $T \rightarrow 0$ near the unconventional quantum critical point in the heavy-fermion metal $\beta$-YbAlB$_4$. The high Kondo temperature $T_K$ $\simeq$ 200 K in this material allows us to probe transport extremely close to the critical point, at unusually small values of $T/T_K < 5 \times 10^{-4}$. Here we find that the Wiedemann-Franz law is obeyed at the lowest temperatures, implying that the Landau quasiparticles remain intact in the critical region. At finite temperatures we observe a non-Fermi liquid T-linear dependence of inelastic scattering processes to energies lower than those previously accessed. These processes have a weaker temperature dependence than in comparable heavy fermion quantum critical systems, and suggest a new temperature scale of $T \sim 0.3 K$ which signals a sudden change in character of the inelastic scattering.