Resistivities of Ceramic and Single-Crystalline Superconducting Oxides to 1100K: What Do They Tell Us?

Resistivities p(T) of ceramic samples of La sub (1.825) Sr sub (0.175) CuO sub 4 (LSCO) and both ceramic and single-crystalline (a-b plane, containing micro-twins) samples of YBa sub 2 Cu sub 3 O sub (7- delta) (YBCO) were measured from the respective transition temperatures T sub c to T = 1100K. Above room temperature measurements were performed in a flowing-O sub 2 furnace. The observed absence of saturation in the linear parts of p(T) to 1100K in LSCO and to 600 K in YBCO implies weak electron-phonon coupling in both superconductors, thus excluding the possibility of phonon-mediated superconductivity.