The Lorenz number in the optimally doped and underdoped Eu-123 superconductor

TL;DR

This study measures the Hall-Lorenz numbers in EuBa2Cu3Oy superconductors before and after oxygen reduction, revealing weak temperature dependence and indications of pseudo-gap behavior in the electronic system.

Contribution

It provides new experimental data on the temperature dependence of Hall-Lorenz numbers in Eu-123 superconductors under different doping conditions.

Findings

Lxy is about twice the Sommerfeld value in both samples.

Lxy weakly depends on temperature between 300-160 K.

Lxy behavior suggests presence of pseudo-gaps in the electronic system.

Abstract

The temperature dependences of the Hall-Lorenz numbers (Lxy) in a EuBa2Cu3Oy (Eu-123) single crystal before and after oxygen reduction are reported. The study is based on data on the normal state longitudinal and transversal transport coefficients. Namely, the temperature dependences of the electrical resistivity, Hall coefficient, longitudinal thermal conductivity, and transverse thermal conductivity are presented. The set of measurements was performed for an optimally doped sample (y = 7), then the oxygen content in the the same crystal was reduced to y = 6.65, and the measurements were repeated. For both cases Lxy's are about two times larger than the Sommerfeld's value of the Lorenz number and depend weakly on temperature in a range 300 - 160 K. Below T = 160 K the Hall-Lorenz number for the optimally doped sample slowly drops, while the value of Lxy for the oxygen reduced sample begins to rise. Such results suggest that the electronic system in the investigated compound may be considered as a metallic one with pseudo-gaps that open at the Fermi level.