The electronic thermal transport in the EuBa2Cu3Oy superconductor

The heat transport properties in the normal state of a high quality EuBa2Cu3Oy single crystal in two oxygen configurations were studied. Measurements of the longitudinal and transverse transport coefficients were performed for an optimally doped sample (y ≈ 7), then the oxygen content in the material was reduced to y ≈ 6.65, and the set of measurements was repeated. The object of investigations was still literally the same crystal. We found the Hall-Lorenz numbers (Lxy) for both specimens behave almost identical in a temperature range 300-160 K, i.e. Lxy's depend weakly on temperature and are about two times larger than the Sommerfeld's value of the Lorenz number (L0). 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. A phenomenological model of the electronic structure containing a pseudo-gap was proposed to explain the observed behaviors. The determined temperature dependences of the Lorenz number have been used to separate the total thermal conductivities for electronic and phonon parts and some conclusions about the scattering mechanisms are withdrawn.