Anisotropic thermopower in single crystals of the high-Tc superconductor YBa2Cu3O7

Abstract

The thermopower in single crystals of Y${\mathrm{Ba}}_2$ ${\mathrm{Cu}}_3$ ${\mathrm{O}}_7$ has quite different behavior in the in-plane ($S_{\mathrm{ab}}$) and out-of-plane ($S_c$) directions. $S_{\mathrm{ab}}$ is positive and shows a characteristic peak above $T_c$ while $S_c$ (also positive) increases strongly with temperature with a dependence which may be fitted to $T^{1.65}$ or $AT+B{T}^2$. We discuss the role of phonon drag and band filling in affecting the sign of the in-plane thermopower.