Enhancement of the Hall-Lorenz number in optimally doped YBa2Cu3O_7-d

TL;DR

This study investigates electronic heat transport in optimally doped YBa2Cu3O7-d, revealing an enhanced Hall-Lorenz number that exceeds the standard value, with interpretations possible via Fermi liquid or bipolaron models.

Contribution

It provides experimental measurements of the Hall-Lorenz number in YBa2Cu3O7-d and discusses its implications for understanding charge transport models in high-temperature superconductors.

Findings

Hall-Lorenz number is about twice the Sommerfeld value.

Weak temperature dependence of the Hall-Lorenz number from 100 to 300 K.

Both Fermi liquid and bipolaron models can explain the observed data.

Abstract

Electronic heat transport in the normal state of a high-quality single crystal of optimally-doped superconductor YBa2Cu3O6.95 was studied by measurements of longitudinal and transverse transport coefficients. For the temperature range from 100 to 300 K, the Hall-Lorenz number (Lxy) depends weakly on temperature and is about two times larger than the Sommerfeld value of the Lorenz number Lo = (pi^2)/3. Our results can be interpreted using a Fermi liquid model when effects of the pseudogap that opens at the Fermi level are included. However, we find that the bipolaron model can also explain both the enhanced value and the weak temperature dependence of the Hall-Lorenz number.