Thermopower of high-T_c cuprates

TL;DR

This study investigates the thermopower behavior of various high-T_c cuprates, revealing anomalies at magnetic transitions and a doping-dependent sign change, suggesting additional contributions beyond standard diffusion thermopower.

Contribution

It provides new insights into the complex thermopower behavior of high-T_c cuprates, highlighting the presence of extra contributions and their relation to doping and magnetic transitions.

Findings

Thermopower shows anomalies at Neel temperatures.

Sign change of thermopower with doping in Bi-based cuprates.

Extra contributions to thermopower beyond diffusion effects.

Abstract

We have studied the thermopower of La_2CuO_{4+z} and Nd_2CuO_{4-y} which undergo an antiferromagnetic transition near room temperature and Bi_2Sr_{2-x}La_xCuO_{6+z} for which a broad spectrum of doping is possible. The thermopower of La_2CuO_{4+z} and Nd_2CuO_{4-y} is seen to exhibit an anomaly at the Neel temperature, whereas the resistivity is not. The extrapolated zero-temperature intercept of the thermopower, which is known to be positive for hole-doped cuprate superconductors, is found to become negative for Bi_2Sr_{2-x}La_xCuO_{6+z} above some critical doping-level. The data strongly suggest that the thermopower of high-T_c cuprates contains a large amount of extra contribution in addition to the usual diffusion thermopower. We discuss origins of the extra contribution in the thermopower.