Thermopower of Cuprate Superconductors under Hydrostatic Pressure

Measurements of thermopower versus temperature under hydrostatic pressure are reported for ${\mathrm{La}}_{2-x}{\mathrm{Sr}}_x{\mathrm{CuO}}_4$ having no charge reservoir and the underdoped ${\mathrm{YBa}}_2{\mathrm{Cu}}_3{\mathrm{O}}_{7-\delta }$, which we demonstrate to have a pressure-induced electron transfer from the ${\mathrm{CuO}}_2$ sheets to the $\mathrm{Cu}\left(1\right){\mathrm{O}}_{1-\delta }$ reservoir planes. The ${\mathrm{CuO}}_2$ sheets exhibit a thermopower $\alpha \left(T\right)={\alpha }_0+\delta \alpha \left(T\right)$ in which $\alpha \approx {\alpha }_0$ at room temperature decreases with increasing hole concentration, and $\delta \alpha \left(T\right)$ is an enhancement having a maximum at $T_{\max }=100\mathrm{}$–140 K. Correlation between ${\mathrm{dT}}_c/dP$ and $d\left(\delta \alpha \right)/dP$ are discussed.