Magnetic heat transport in R${}_2$CuO${}_4$ (R = La, Pr, Nd, Sm, Eu, and Gd)

Abstract

We have studied the thermal conductivity $\hat{I}º$ on single crystalline samples of the antiferromagnetic monolayer cuprates R${}_2$CuO${}_4$ with R = La, Pr, Nd, Sm, Eu, and Gd. For a heat current within the CuO${}_2$ planes, i.e. for $\hat{I}{º}_{ab}$ we find high-temperature anomalies around 250 K in all samples. In contrast, the thermal conductivity $\hat{I}{º}_c$ perpendicular to the CuO${}_2$ planes, which we measured for R = La, Pr, and Gd, shows a conventional temperature dependence as expected for a purely phononic thermal conductivity. This qualitative anisotropy of $\hat{I}{º}_i$ and the anomalous temperature dependence of $\hat{I}{º}_{ab}$ give evidence for a significant magnetic contribution $\hat{I}{º}_{mag}$ to the heat transport within the CuO${}_2$ planes. Our results suggest, that a large magnetic contribution to the heat current is a common feature of single-layer cuprates. We find that $\hat{I}{º}_{mag}$ is hardly affected by structural instabilities, whereas already weak charge carrier doping causes a strong suppression of $\hat{I}{º}_{mag}$.

7 pages, 4 figures