Systematics in the thermoelectric power of high-${\mathit{T}}_{\mathit{c}}$ oxides

Many superconducting cuprates show a parabolic variation of ${\mathit{T}}_{\mathit{c}}$ with hole concentration p, there being a minimum and a maximum hole concentration for superconductivity. Thermoelectric power (TEP) measurements reported here as a function of p for a number of oxides reveal several important trends: (1) close similarities in the TEP of several compounds and a change in sign of the room-temperature TEP near the maximum ${\mathit{T}}_{\mathit{c}}$, (2) continuity in the TEP when doping across the two superconducting-nonsuperconducting boundaries, and (3) a universal correspondence of the room-temperature TEP with p over the whole range of doping.