Heat transport of La$_{2-y}$Eu$_y$CuO$_4$ and La$_{1.88-y}$Eu$_y$Sr$_{0.12}$CuO$_4$ single crystals

TL;DR

This study investigates how Eu doping affects phonon heat transport in La-based cuprates, revealing complex doping-dependent behaviors and the role of stripe phases in phonon scattering mechanisms.

Contribution

It provides new insights into the impact of Eu doping on phonon heat transport and the role of stripe phases versus structural changes in La-based cuprates.

Findings

Eu doping suppresses and then reappears in phonon peaks depending on concentration.

Eu doping enhances phonon transport in charge-doped La$_{1.88}$Sr$_{0.12}$CuO$_4$.

Stripe phases influence phonon scattering more than structural distortions.

Abstract

To study the rare-earth doping effect on the phonon heat transport of La-based cuprates and shed light on the mechanism of phonon scattering, both $ab$-plane and c-axis thermal conductivities ($\kappa_{ab}$ and $\kappa_c$) are measured for La$_{2-y}$Eu$_y$CuO$_4$ ($y$ = 0, 0.02 and 0.2) and La$_{1.88-y}$Eu$_y$Sr$_{0.12}$CuO$_4$ ($y$ = 0 and 0.2) single crystals. It is found that the phonon peak (at 20 -- 25 K) in $\kappa_{ab}(T)$ of La$_{2-y}$Eu$_y$CuO$_4$ shows an anomalous Eu-doping dependence: it completely disappears for $y$ = 0.02, which is discussed to be due to the local lattice distortions around Eu dopants, and reappears for $y$ = 0.2 with much smaller peak magnitude compared to $y$ = 0 sample. In contrast to the strong suppression of the phonon peak in Eu-doped La$_2$CuO$_4$, Eu-doping to La$_{1.88}$Sr$_{0.12}$CuO$_4$ enhances the low-$T$ phonon heat transport that results in the reappearance of the phonon peak in this charge-carrier-doped system. The data clearly show that the establishment of static stripe phase rather than the structural change is responsible for the reappearance of phonon peak.